TWI871293B - Light-emitting element, light-emitting device, display device, electronic device and lighting device - Google Patents

Abstract

A light-emitting element with high light-emitting efficiency and reliability is provided. One embodiment of the present invention is a light-emitting element including a host material and a guest material in a light-emitting layer. The host material has a function of converting triplet excitation energy into light-emitting, and the guest material emits fluorescence. The molecular structure of the guest material is a structure having a luminophore and a protecting group, and the guest material molecule has five or more protecting groups. By introducing the protecting group into the molecule, the transfer of triplet excitation energy from the host material to the guest material based on the Dexter mechanism is suppressed. As the protecting group, an alkyl group or a branched alkyl group is used. By using a material having a five-membered ring skeleton as the host material, a light-emitting element with further improved light-emitting efficiency can be obtained.

Description

Light-emitting element, light-emitting device, display device, electronic device and lighting device

An embodiment of the present invention relates to a light-emitting element or a display device, an electronic machine and a lighting device including the light-emitting element.

Note that an embodiment of the present invention is not limited to the above-mentioned technical fields. The technical field of an embodiment of the invention disclosed in this specification and the like is related to an object, a method or a manufacturing method. In addition, an embodiment of the present invention is related to a process, a machine, a product or a composition of matter. Therefore, to be more specific, examples of the technical field of an embodiment of the present invention disclosed in this specification include semiconductor devices, display devices, liquid crystal display devices, light-emitting elements, lighting devices, power storage devices, memory devices, driving methods of these devices or manufacturing methods of these devices.

In recent years, research and development of light-emitting devices using electroluminescence (EL) have become increasingly intense. The basic structure of these light-emitting devices is a structure in which a layer containing a light-emitting substance (EL layer) is sandwiched between a pair of electrodes. By applying a voltage between the electrodes of the device, light from the light-emitting substance can be obtained.

In particular, since the light-emitting element is a self-luminous light-emitting element, a display device using the light-emitting element has the following advantages: good visibility, no need for backlight, low power consumption, etc. In addition, it also has the following advantages: it can be made thin and light, and has a fast response speed, etc.

When a light-emitting element (e.g., an organic EL element) is used in which an organic compound is used as a light-emitting substance and an EL layer containing the light-emitting substance is provided between a pair of electrodes, by applying a voltage between the pair of electrodes, electrons and holes are injected from the cathode and the anode into the light-emitting EL layer, respectively, so that a current flows. Then, the injected electrons and holes are recombined to make the light-emitting organic compound into an excited state, so that light can be obtained from the excited light-emitting organic compound.

There are two types of excited states formed by organic compounds: singlet excited state (S ^* ) and triplet excited state (T ^* ). The emission from the singlet excited state is called fluorescence, and the emission from the triplet excited state is called phosphorescence. In addition, in a light-emitting element, the statistical generation ratio of the singlet excited state and the triplet excited state is considered to be S ^* :T ^* = 1:3. Therefore, the light-emitting efficiency of a light-emitting element using a phosphorescent compound (phosphorescent material) is higher than that of a light-emitting element using a fluorescent compound (fluorescent material). Therefore, in recent years, research and development of light-emitting elements using phosphorescent materials that can convert triplet excited energy into light emission has become increasingly hot.

Among light-emitting elements using phosphorescent materials, especially light-emitting elements emitting blue light, it is difficult to develop stable compounds with high triplet excitation energy levels, so they have not yet been put into practical use. Therefore, light-emitting elements using more stable fluorescent materials are being developed, and methods for improving the light-emitting efficiency of light-emitting elements using fluorescent materials (fluorescent light-emitting elements) are being sought.

As a material capable of converting part or all of triplet excitation energy into luminescence, in addition to phosphorescent materials, thermally activated delayed fluorescence (TADF) materials are known. In TADF materials, a singlet excited state is generated from a triplet excited state by reverse intersystem crossing, and the singlet excited state is converted into luminescence.

In order to improve the luminescence efficiency in a light-emitting element using a thermally activated delayed fluorescence material, it is important not only to efficiently generate a singlet excited state from a triplet excited state in the thermally activated delayed fluorescence material, but also to efficiently obtain luminescence from the singlet excited state, that is, to have a high fluorescence quantum yield. However, it is difficult to design a light-emitting material that satisfies both of the above conditions.

In addition, a method has been proposed in which, in a light-emitting element including a heat-activated delayed fluorescent material and a fluorescent material, the singlet excitation energy of the heat-activated delayed fluorescent material is transferred to the fluorescent material, and luminescence is obtained from the fluorescent material (see Patent Document 1). That is, a light-emitting element using the heat-activated delayed fluorescent material as a host material and the fluorescent material as a guest material has been proposed.

[Patent Document 1] Japanese Patent Application Publication No. 2014-45179

As a method for achieving high efficiency of a fluorescent light-emitting element, for example, the following method can be cited: in a light-emitting layer including a host material and a guest material, the triplet excitation energy contained in the host material is converted into singlet excitation energy, and then the singlet excitation energy is transferred to the fluorescent material as the guest material. However, the process of converting the triplet excitation energy of the host material into the singlet excitation energy competes with the process of deactivating the triplet excitation energy. Therefore, sometimes the conversion of the triplet excitation energy of the host material to the singlet excitation energy is insufficient. For example, as a path for deactivating the triplet excitation energy, the following deactivation path is considered: when a fluorescent material is used as a guest material in the light-emitting layer of a light-emitting element, the triplet excitation energy of the host material is transferred to the lowest triplet excitation energy level ( _T1 level) of the fluorescent material. Energy transfer through this deactivation path does not contribute to luminescence, thus resulting in a decrease in the luminescence efficiency of the fluorescent light-emitting element. Although this deactivation path can be suppressed by reducing the concentration of the guest material, the energy transfer rate from the host material to the singlet excited state of the guest material also slows down. Therefore, quenching due to deterioration or impurities is likely to occur. As a result, the brightness of the light-emitting element is easily reduced, which leads to a decrease in reliability.

Therefore, an embodiment of the present invention aims to suppress the transfer of the triplet excitation energy of the host material to the _T1 energy level of the guest material in the host material and the guest material of the light-emitting layer included in the light-emitting element, efficiently convert the triplet excitation energy of the host material into the singlet excitation energy of the guest material, improve the fluorescent luminescence efficiency of the light-emitting element, and improve the reliability.

An object of one embodiment of the present invention is to provide a light-emitting element with high light-emitting efficiency. In addition, an object of one embodiment of the present invention is to provide a light-emitting element with high reliability. In addition, an object of one embodiment of the present invention is to provide a light-emitting element with reduced power consumption. In addition, an object of one embodiment of the present invention is to provide a novel light-emitting element. In addition, an object of one embodiment of the present invention is to provide a novel light-emitting machine. In addition, an object of one embodiment of the present invention is to provide a novel display device.

In addition, the description of the above-mentioned purpose does not hinder the existence of other purposes. Note that one embodiment of the present invention does not need to achieve all of the above-mentioned purposes. In addition, purposes other than the above-mentioned purposes can be clearly seen from the description of the specification, drawings, patent application scope, etc., and purposes other than the above-mentioned purposes can be derived from the description of the specification, drawings, patent application scope, etc.

One embodiment of the present invention provides a light-emitting element, which is mainly capable of suppressing energy transfer based on the Dexter mechanism in energy transfer between a host material (energy donor) and a guest material (energy acceptor), so as to suppress the transfer of triplet excitation energy of the host material to the _T1 energy level of the guest material in the light-emitting layer included in the light-emitting element.

In order to suppress the energy transfer based on the Dexter mechanism, it is preferable to separate the energy donor and the energy acceptor in the light-emitting layer in such a way that the energy transfer does not occur. Therefore, one embodiment of the present invention provides a light-emitting element, which uses an energy donor having a bulky structure and an energy acceptor with a protective group so that the light-emitting body contained in the energy donor and the light-emitting body contained in the energy acceptor are separated in such a way that the energy transfer does not occur. In addition, in one embodiment of the present invention, the triple energy level (T1 energy level) possessed by the energy donor is preferably higher than the single energy level (S1 energy level) possessed by the energy acceptor.

In one embodiment of the present invention, a material having a substituent in a five-membered ring skeleton is used as an energy donor having a bulky structure. In addition, a fluorescent material is used as an energy acceptor, and the fluorescent material has a bulky structure due to having a protective group. As the five-membered ring skeleton of the energy donor, an imidazole skeleton or a triazole skeleton is particularly preferably used.

Thus, one embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer comprises a first material and a second material, the first material being capable of converting triplet excitation energy into light-emitting and having a five-membered ring skeleton, the second material being capable of converting singlet excitation energy into light-emitting and having a light-emitting body and five or more protecting groups, the light-emitting body being a condensed aromatic ring or a condensed heteroaromatic ring, the five or more protecting groups independently having any one of an alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 12 carbon atoms, the T1 energy level of the first material being higher than the S1 energy level of the second material.

In the above structure, preferably, at least four of the five or more protecting groups are independently any one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms.

In addition, another embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material and a second material, the first material can convert triplet excitation energy into light-emitting and has a five-membered ring skeleton, the second material can convert singlet excitation energy into light-emitting and has a light-emitting body and at least four protecting groups, the light-emitting body is a fused aromatic ring or a fused heteroaromatic ring, the four protecting groups are not directly bonded to the fused aromatic ring or the fused heteroaromatic ring, the four protecting groups independently have any one of an alkyl group with a carbon number of 3 to 10, a substituted or unsubstituted cycloalkyl group with a carbon number of 3 to 10, and a trialkylsilyl group with a carbon number of 3 to 12, and the T1 energy level of the first material is higher than the S1 energy level of the second material.

In addition, another embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material and a second material, the first material can convert triplet excitation energy into light emission and has a five-membered ring skeleton, the second material can convert singlet excitation energy into light emission and has a light emitter and two or more diarylamine groups, the light emitter is a fused aromatic ring or a fused heteroaromatic ring, the fused aromatic ring or the fused heteroaromatic ring has a bond The first material is compounded with two or more diarylamine groups, the aryl groups in the two or more diarylamine groups each independently have at least one protecting group, the protecting groups each independently have any one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 12 carbon atoms, and the T1 energy level of the first material is higher than the S1 energy level of the second material.

In addition, another embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material and a second material, the first material can convert triplet excitation energy into light emission and has a five-membered ring skeleton, the second material can convert singlet excitation energy into light emission and has a light emitter and two or more diarylamine groups, the light emitter is a fused aromatic ring or a fused heteroaromatic ring, the fused aromatic ring or the fused heteroaromatic ring has a bond The first material is compounded with two or more diarylamine groups, and the aryl groups in the two or more diarylamine groups independently have at least two protecting groups, and the protecting groups independently have any one of an alkyl group with a carbon number of not less than 3 and not more than 10, a substituted or unsubstituted cycloalkyl group with a carbon number of not less than 3 and not more than 10, and a trialkylsilyl group with a carbon number of not less than 3 and not more than 12, and the T1 energy level of the first material is higher than the S1 energy level of the second material.

In the above structure, the diarylamine group is preferably a diphenylamine group.

In addition, another embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material and a second material, the first material is capable of converting triplet excitation energy into light emission and has a five-membered ring skeleton, the second material is capable of converting singlet excitation energy into light emission and has a light-emitting body and a plurality of protecting groups, the protecting groups independently have an alkyl group with a carbon number of not less than 3 and not more than 10, a substituted or unsubstituted carbon number of 3 Any one of a cycloalkyl group having more than and less than 10 carbon atoms and a trialkylsilyl group having more than 3 and less than 12 carbon atoms, the luminescent body is a fused aromatic ring or a fused heteroaromatic ring, at least one of the atoms constituting the protecting group is located directly on the surface of one of the fused aromatic ring and the fused heteroaromatic ring, at least one of the atoms constituting the plurality of protecting groups is located directly on the surface of another of the fused ring and the fused heteroaromatic ring, and the T1 energy level of the first material is higher than the S1 energy level of the second material.

In addition, another embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material and a second material, the first material can convert triplet excitation energy into light emission and has a five-membered ring skeleton, the second material can convert singlet excitation energy into light emission and has a light emitter and two or more diphenylamine groups, the light emitter is a fused aromatic ring or a fused heteroaromatic ring, the fused aromatic ring or the fused heteroaromatic ring is bonded to In two or more diphenylamine groups, the phenyl groups in the two or more diphenylamine groups independently have protecting groups at the 3-position and the 5-position, and the protecting groups independently have any one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 12 carbon atoms, and the T1 energy level of the first material is higher than the S1 energy level of the second material.

In the above structure, the five-membered ring skeleton is preferably any one of a pyrazole skeleton, an imidazole skeleton and a triazole skeleton, and more preferably, the nitrogen atom unrelated to the double bond of the imidazole skeleton and the triazole skeleton has a substituted or unsubstituted aromatic group having 6 to 13 carbon atoms.

In addition, another embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material and a second material, the first material can convert triplet excitation energy into light emission and has a five-membered ring skeleton, the second material can convert singlet excitation energy into light emission and has a light-emitting body and two or more protecting groups, the light-emitting body is a fused aromatic ring or a fused heteroaromatic ring, and the two or more protecting groups each independently have a carbon atom number of 1 or more and 10 or less. Any one of an alkyl group, a substituted or unsubstituted cycloalkyl group with a carbon number of 3 or more and 10 or less, and a trialkylsilyl group with a carbon number of 3 or more and 12 or less, the first material has a five-membered ring skeleton, the five-membered ring skeleton has at least one of an imidazole skeleton and a triazole skeleton, the nitrogen atoms unrelated to the double bond of the imidazole skeleton and the triazole skeleton have a substituted or unsubstituted aromatic group with a carbon number of 6 to 13, and the T1 energy level of the first material is higher than the S1 energy level of the second material.

In the above structure, the aromatic hydrocarbon group is preferably a phenyl group.

In the above structure, the alkyl group is preferably a branched alkyl group.

In addition, in the above structure, the branched alkyl group preferably contains a quaternary carbon.

In the above structure, the condensed aromatic ring or condensed heteroaromatic ring preferably includes any one of naphthalene, anthracene, fluorene, chrysene, triphenylene, pyrene, tetraphenylene, perylene, coumarin, quinacridone and naphthodibenzofuran.

In addition, in the above structure, the light-emitting layer preferably further includes a third material, and the first material and the third material preferably form an excited state complex.

In the above structure, the emission spectrum of the excited complex preferably overlaps with the absorption band on the longest wavelength side of the second material.

In the above structure, the five-membered ring skeleton preferably has any one of a pyrazole skeleton, an imidazole skeleton and a triazole skeleton.

In the above structure, the first material is preferably a metal complex. In addition, more preferably, the metal complex contains metals of groups 8 to 10 and periods 5 and 6, and a five-membered ring skeleton is coordinated to the metal.

In addition, in the above structure, the first material preferably emits phosphorescence.

In addition, in the above structure, the emission spectrum of the first material preferably overlaps with the absorption band on the longest wavelength side of the second material.

In addition, in the above structure, the concentration of the second material in the light-emitting layer is preferably greater than 2 wt % and less than 30 wt %.

In addition, another embodiment of the present invention is a light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer has an energy donor and an energy acceptor, the energy acceptor has the function of converting triplet excitons into light emission, the energy acceptor has a five-membered ring skeleton, the energy acceptor has a light-emitting body and five or more protecting groups, the light-emitting body is a condensed aromatic ring or a condensed heteroaromatic ring, the five or more protecting groups independently have any one of an alkyl group with a carbon number of 1 to 10, a substituted or unsubstituted cycloalkyl group with a carbon number of 3 to 10, and a trialkylsilyl group with a carbon number of 3 to 12, the T1 energy level of the energy donor is higher than the S1 energy level of the energy acceptor, the triplet excitation energy of the energy donor is converted into the singlet excitation energy of the energy acceptor, and light emission from the energy acceptor can be obtained.

In the above structure, the luminescence originating from the energy acceptor is preferably fluorescent luminescence.

In addition, another embodiment of the present invention is a display device including a light-emitting element of each of the above-mentioned structures, and at least one of a color filter and a transistor. Another embodiment of the present invention is an electronic device including: the display device; and at least one of a housing and a touch sensor. In addition, another embodiment of the present invention is a lighting device including: a light-emitting element of each of the above-mentioned structures; and at least one of a housing and a touch sensor. In addition, an embodiment of the present invention includes an electronic device including a light-emitting element in addition to a light-emitting device including a light-emitting element. Therefore, the light-emitting device in this specification refers to an image display device or a light source (including a lighting device). In addition, the light-emitting device sometimes also includes the following modules: a display module in which a connector such as FPC (Flexible Printed Circuit) or TCP (Tape Carrier Package) is installed in the light-emitting element; a display module in which a printed circuit board is provided at the end of the TCP; or a display module in which an IC (integrated circuit) is directly mounted on the light-emitting element by COG (Chip On Glass).

According to an embodiment of the present invention, a light-emitting element with high light-emitting efficiency can be provided. In addition, according to an embodiment of the present invention, a light-emitting element with high reliability can be provided. In addition, according to an embodiment of the present invention, a light-emitting element with reduced power consumption can be provided. In addition, according to an embodiment of the present invention, a novel light-emitting element can be provided. In addition, according to an embodiment of the present invention, a novel light-emitting machine can be provided. In addition, according to an embodiment of the present invention, a novel display device can be provided. In addition, according to an embodiment of the present invention, a novel organic compound can be provided.

Note that the description of these effects does not hinder the existence of other effects. In addition, one embodiment of the present invention does not necessarily need to have all of the above effects. In addition, effects other than the above effects can be known and derived from the description of the specification, drawings, patent application scope, etc.

The following is a detailed description of the embodiments of the present invention with reference to the drawings. Note that the present invention is not limited to the following description, and its methods and details can be transformed into various forms without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the embodiments shown below and the contents recorded in the examples.

In addition, the positions, sizes, ranges, etc. of each structure shown in the drawings and the like may not represent actual positions, sizes, ranges, etc. for easy understanding. Therefore, the disclosed invention is not necessarily limited to the positions, sizes, ranges, etc. disclosed in the drawings and the like.

In addition, in this specification, for the sake of convenience, ordinal numbers such as first and second are added, but they sometimes do not indicate the process order or stacking order. Therefore, for example, "first" can be appropriately replaced with "second" or "third" for description. In addition, the ordinal numbers recorded in this specification and the like are sometimes inconsistent with the ordinal numbers used to specify an embodiment of the present invention.

Note that in this specification and the like, when describing the structure of the invention using drawings, symbols representing the same parts may be used in common in different drawings.

In this specification, "film" and "layer" may be interchanged. For example, "conductive layer" may be interchanged with "conductive film". Also, "insulating film" may be interchanged with "insulating layer".

In addition, in this specification, etc., a singlet excited state (S ^* ) refers to a singlet state having excitation energy. In addition, an S1 energy level is the lowest energy level of the singlet excited energy level, which refers to the excitation energy level of the lowest singlet excited state (S1 state). In addition, a triplet excited state (T ^* ) refers to a triplet state having excitation energy. In addition, a T1 energy level is the lowest energy level of the triplet excited energy level, which refers to the excitation energy level of the lowest triplet excited state (T1 state). In addition, in this specification, etc., even if simply expressed as "singlet excited state" and "singlet excited state energy level", sometimes the S1 state and the S1 energy level are respectively expressed. In addition, even if expressed as "triplet excited state" and "triplet excited state energy level", sometimes the T1 state and the T1 energy level are respectively expressed.

In this specification, a fluorescent material refers to a compound that emits light in the visible light region when returning from a singlet excited state to a ground state. A phosphorescent material refers to a compound that emits light in the visible light region at room temperature when returning from a triplet excited state to a ground state. In other words, a phosphorescent material refers to one of the compounds that can convert triplet excited energy into visible light.

In this specification, etc., the blue wavelength region refers to a wavelength region of 400 nm or more and less than 490 nm, and blue luminescence has at least one emission spectrum peak in this wavelength region. In addition, the green wavelength region refers to a wavelength region of 490 nm or more and less than 580 nm, and green luminescence has at least one emission spectrum peak in this wavelength region. In addition, the red wavelength region refers to a wavelength region of 580 nm or more and less than 680 nm, and red luminescence has at least one emission spectrum peak in this wavelength region.

Implementation method 1 In this implementation method, a light-emitting element of an implementation method of the present invention is described with reference to FIGS. 1A to 5C.

First, the structure of a light emitting element according to an embodiment of the present invention will be described with reference to FIGS. 1A to 1C .

FIG. 1A is a cross-sectional view of a light emitting element 150 according to an embodiment of the present invention.

The light emitting element 150 includes a pair of electrodes (electrode 101 and electrode 102 ) and includes an EL layer 100 disposed between the pair of electrodes. The EL layer 100 includes at least a light emitting layer 130 .

In addition, the EL layer 100 shown in FIG. 1A includes functional layers such as a hole injection layer 111 , a hole transport layer 112 , an electron transport layer 118 , and an electron injection layer 119 in addition to the light-emitting layer 130 .

Note that although the present embodiment describes the electrode 101 of a pair of electrodes as an anode and the electrode 102 as a cathode, the structure of the light-emitting element 150 is not limited thereto. In other words, the electrode 101 may be used as a cathode and the electrode 102 may be used as an anode, and the layers between the electrodes may be stacked in reverse order. In other words, the hole injection layer 111, the hole transport layer 112, the light-emitting layer 130, the electron transport layer 118, and the electron injection layer 119 may be stacked in sequence from the anode side.

Note that the structure of the EL layer 100 is not limited to the structure shown in FIG. 1A , as long as it includes at least one selected from the hole injection layer 111, the hole transport layer 112, the electron transport layer 118, and the electron injection layer 119. Alternatively, the EL layer 100 may include a functional layer having the following functions: reducing the injection barrier of holes or electrons; improving the transport properties of holes or electrons; blocking the transport properties of holes or electrons; or suppressing the quenching phenomenon caused by the electrode, etc. The functional layer may be a single layer or a structure in which a plurality of layers are stacked.

<Luminescence mechanism of the luminescent element> Next, the luminescence mechanism of the luminescent layer 130 will be described.

In the light-emitting element 150 of one embodiment of the present invention, by applying a voltage between a pair of electrodes (electrode 101 and electrode 102), electrons and holes are injected from the cathode and anode into the EL layer 100, respectively, so that a current flows. Among the excitons generated by the recombination of carriers (electrons and holes), the statistical probability of the ratio of singlet excitons to triplet excitons (hereinafter referred to as the exciton generation probability) is 1:3. That is, the proportion of singlet excitons generated is 25%, and the proportion of triplet excitons generated is 75%. Therefore, in order to improve the light-emitting efficiency of the light-emitting element, it is important to make triplet excitons contribute to light emission. Therefore, as the light-emitting layer 130, it is preferable to use a material having the function of converting triplet excitation energy into light emission.

As a material having the function of converting triplet excitation energy into luminescence, a compound capable of emitting phosphorescence (hereinafter referred to as a phosphorescent material) can be cited. In this specification, etc., a phosphorescent material refers to a compound that emits phosphorescence but not fluorescence at any temperature in the temperature range of above the low temperature obtained by liquid nitrogen (e.g., 77K) and below room temperature. The phosphorescent material preferably contains a metal element with a large spin-orbit interaction, specifically, preferably contains a transition metal element, particularly preferably contains a platinum group element (element of the 8th to 10th and 5th and 6th periods (ruthenium (Ru), rhodium (Rh), palladium (Pd), niobium (Os), iridium (Ir) or platinum (Pt)), and particularly preferably contains iridium. Iridium can increase the transition probability of the direct transition between the singlet ground state and the triplet excited state, so it is preferred.

In addition, as a material having the function of converting triplet excitation energy into light emission, TADF materials can be cited. TADF materials refer to materials that have a small difference between the S1 energy level and the T1 energy level and have the function of converting triplet excitation energy into singlet excitation energy by antisystem crossing. Therefore, it is possible to up-convert triplet excitation energy into singlet excitation energy (antisystem crossing) by using tiny thermal energy (room temperature, etc.) and efficiently generate a singlet excited state. Exciplexes that form excited states with two substances have the function of TADF materials that convert triplet excitation energy into singlet excitation energy because the difference between the S1 energy level and the T1 energy level is extremely small.

As an indicator of the T1 energy level, the phosphorescence spectrum observed at a low temperature (e.g., 10 K) can be used. For TADF materials, it is preferred that a tangent line is drawn at the tail of the short-wavelength side of the fluorescence spectrum, and the energy of the wavelength of the extrapolated line is set to the S1 energy level, and a tangent line is drawn at the tail of the short-wavelength side of the phosphorescence spectrum, and the energy of the wavelength of the extrapolated line is set to the T1 energy level. At this time, the difference between S1 and T1 is less than 0.2 eV.

FIG1B is a schematic cross-sectional view of a light-emitting layer 130 of a light-emitting element of an embodiment of the present invention. In an embodiment of the present invention, the light-emitting layer 130 comprises compound 131, compound 132 and compound 133. Compound 133 has a function of converting triplet excitation energy into luminescence and has a five-membered ring skeleton. Compound 132 has a function of converting singlet excitation energy into luminescence and has a protecting group. Since the stability of the fluorescent material is high, it is preferred to use a fluorescent material as compound 132 to obtain a light-emitting element with high reliability. Compound 131 is a host material, and it is preferred to recombine the carrier on compound 131. Therefore, preferably, in the light-emitting element of one embodiment of the present invention, the singlet excitation energy and triplet excitation energy of the excitons generated by the recombination of carriers in compound 131 are ultimately transferred to the singlet excited state of compound 132 through compound 133, and compound 132 emits light. Here, in the light-emitting layer 130, compound 133 is an energy donor and compound 132 is an energy acceptor. In FIG1B , the light-emitting layer 130 is a fluorescent light-emitting layer having compound 131 as a host material and compound 132 as a guest material. In addition, compound 133 is used as an energy donor. In addition, the light-emitting layer 130 can obtain light emission from compound 132 as a guest material.

<Structural example 1 of the light-emitting layer> Figure 1C shows an example of the energy level correlation in the light-emitting layer 130 of the light-emitting element 150 of one embodiment of the present invention. The light-emitting layer 130 in Figure 1B includes compound 131, compound 132, and compound 133. In one embodiment of the present invention, compound 132 is a fluorescent material having a protective group. Compound 133 has a function of converting triplet excitation energy into luminescence. In this structural example, the explanation is based on the premise that compound 133 is a phosphorescent material.

In addition, FIG1C shows the energy level correlation of compound 131 and compound 132 in the light-emitting layer 130. Note that the description and symbols in FIG1C represent the following: • Comp(131): compound 131 • Comp(133): compound 133 • Guest(132): compound 132 • _SC1 : S1 energy level of compound 131 • _TC1 : T1 energy level of compound 131 • _TC3 : T1 energy level of compound 133 • _TG : T1 energy level of compound 132 • _SG : S1 energy level of compound 132

In the light-emitting element of one embodiment of the present invention, since the recombination of carriers mainly occurs in the compound 131 included in the light-emitting layer 130, singlet excitons and triplet excitons are generated. Since the compound 133 here is a phosphorescent material, by selecting a material that satisfies the relationship of T _C3 ≤ _{T C1} , both the singlet excitation energy and triplet excitation energy generated in the compound 131 can be transferred to the T _C3 energy level of the compound 133 (path A ₁ in FIG. 1C ). Note that some carriers may recombine in the compound 133.

The phosphorescent material used in the above structure preferably contains heavy atoms such as Ir, Pt, Os, Ru, Pd, etc. As described above, in the present structural example, the phosphorescent material is also used as an energy donor, so its quantum yield can be either high or low. When the phosphorescent material is used as compound 133 (energy donor), the energy transfer from the triplet excitation energy level of the energy donor to the singlet excitation energy level of the guest material (energy acceptor) is an allowed transition, so it is preferred. Therefore, the triplet excitation energy of compound 133 can be transferred to the S1 energy level ( _SG ) of compound 132 of the guest material through the process of path _A2 . In path _A2 , compound 133 is used as an energy donor and compound 132 is used as an energy acceptor. At this time, when _TC3 ≥ _SG is satisfied, the excitation energy of compound 133 is efficiently transferred to the singlet excited state of compound 132 as the guest material, so it is preferred. Specifically, it is preferred that a tangent line is drawn at the tail of the short wavelength side of the phosphorescence spectrum of compound 133, and the energy of the wavelength of its extrapolated line is set to _TC3 , and a tangent line is drawn at the wavelength of the absorption end of the absorption spectrum of compound 132 or the tail of the shortest wavelength side of the emission spectrum, and the energy of the wavelength of its extrapolated line is set to _SG , and _TC3 ≥ _SG is satisfied at this time.

Here, in the light-emitting layer 130, compound 131, compound 132, and compound 133 are mixed together. Therefore, there is a possibility that the triplet excitation energy of compound 133 is converted into the triplet excitation energy of compound 132 in competition with the above-mentioned paths _A1 and _A2 (path _A3 in FIG. 1C ). Since compound 132 is a fluorescent material, the triplet excitation energy of compound 132 does not contribute to luminescence. That is, when the energy transfer of path _A3 occurs, the luminescence efficiency of the light-emitting element decreases. Note that, in reality, as the energy transfer from _TC3 to _TG (path _A3 ), there may be a path that is not direct but becomes _TG by internal conversion once the energy is transferred to the triplet excited state higher than _TG of compound 132, but this process is omitted in the figure. The undesirable thermal deactivation process in the following description, i.e. the energy transfer process to _TG, is the same.

Here, as the intermolecular energy transfer mechanism, fluorescence resonance energy transfer (FRET: Fluorescence Resonance Energy Transfer, also called Förster mechanism (dipole-dipole interaction)) and Dexter mechanism (electron exchange interaction) are known. Since compound 132, which is an energy acceptor, is a fluorescent material, the Dexter mechanism is dominant in the energy transfer of path A _3. In general, the Dexter mechanism occurs significantly when the distance between compound 131, which is an energy donor, and compound 132, which is an energy acceptor, is less than 1 nm. Therefore, in order to suppress path A ₃ , it is important to make the distance between the host material and the guest material, that is, the distance between the energy donor and the energy acceptor long.

Since the direct transition from the singlet ground state to the triplet excited state in compound 132 is a forbidden transition, the energy transfer from the singlet excited energy level (S _C1 ) of compound 131 to the triplet excited energy level ( _TG ) of compound 132 is unlikely to become a major energy transfer process and is therefore not shown.

Most of the _TG in FIG1C is derived from the energy level of the luminophore in the energy acceptor. Therefore, in more detail, in order to suppress the path _A3 , it is important to lengthen the distance between the energy donor and the luminophore included in the energy acceptor. As a method for lengthening the distance between the energy donor and the luminophore included in the energy acceptor, reducing the concentration of the energy acceptor in the mixed film of these compounds is generally cited. However, when the concentration of the energy acceptor in the mixed film is reduced, in addition to the energy transfer based on the Dexter mechanism from the energy donor to the energy acceptor, the energy transfer based on the Foster mechanism is also suppressed. At this time, because the path _A2 is based on the Foster mechanism, problems such as a reduction in the luminous efficiency of the light-emitting element or a reduction in reliability occur.

Therefore, the inventors of the present invention have found that the above-mentioned decrease in luminescence efficiency can be suppressed by using a fluorescent material having a protective group for increasing the distance between the fluorescent material and the energy donor as an energy acceptor. By having a protective group, the fluorescent material can be used as a large energy acceptor.

<Concept of fluorescent material with protective group> FIG. 2A shows a schematic diagram of a fluorescent material without protective group as a general fluorescent material dispersed in a host material as a guest material, and FIG. 2B shows a schematic diagram of a fluorescent material with protective group dispersed in a host material as a guest material of a light-emitting element used in one embodiment of the present invention. The host material can be referred to as an energy donor and the guest material can be referred to as an energy acceptor. Here, the protective group has a function of lengthening the distance between the luminescent body and the host material. In FIG. 2A, the guest material 301 has a luminescent body 310. The guest material 301 is used as an energy acceptor. On the other hand, in FIG. 2B, the guest material 302 includes a luminescent body 310 and a protective group 320. In FIG. 2A and FIG. 2B , the guest material 301 and the guest material 302 are surrounded by the host material 330. In FIG. 2A , because the distance between the luminescent body and the host material is short, energy transfer based on the Foster mechanism (path B ₁ in FIG. 2A and FIG. 2B ) and energy transfer based on the Dexter mechanism (path B ₂ in FIG. 2A and FIG. 2B ) may occur as energy transfer from the host material 330 to the guest material 301. When the energy transfer of triplet excitation energy from the host material to the guest material based on the Dexter mechanism occurs to generate a triplet excited state of the guest material, in the case where the guest material is a fluorescent material, non-radiative deactivation of the triplet excitation energy occurs, which becomes one of the reasons for the decrease in luminescence efficiency.

On the other hand, in FIG2B , the guest material 302 has a protective group 320. Therefore, the distance between the light-emitting body 310 and the host material 330 can be made long. Therefore, the energy transfer based on the Dexter mechanism (path B ₂ ) can be suppressed.

Here, in order to make the object material 302 emit light, the object material 302 needs to receive energy from the host material 330 based on the Foster mechanism because the Dexter mechanism is suppressed. That is, it is better to efficiently utilize the energy transfer based on the Foster mechanism while suppressing the energy transfer based on the Dexter mechanism. It is known that the energy transfer based on the Foster mechanism is also affected by the distance between the host material and the object material. Generally speaking, when the distance between the host material 330 and the light-emitting body 310 of the object material 302 is less than 1nm, the Dexter mechanism is dominant, and when it is greater than 1nm and less than 10nm, the Foster mechanism is dominant. Generally speaking, when the distance between the host material 330 and the light-emitting body 310 of the object material 302 is greater than 10nm, energy transfer is not easy to occur.

Therefore, the protective base 320 preferably diffuses within a range of 1 nm to 10 nm from the luminescent body 310. More preferably, it diffuses within a range of 1 nm to 5 nm from the luminescent body 310. By adopting this structure, energy transfer based on the Dexter mechanism can be efficiently utilized while suppressing energy transfer based on the Foster mechanism from the host material 330 to the guest material 302. Therefore, a light-emitting element with high light-emitting efficiency can be manufactured.

In addition, in order to improve the energy transfer efficiency based on the Foster mechanism (increase the energy transfer speed), it is preferable to increase the concentration of the guest material 301 or the guest material 302 relative to the host material 330. However, generally, when the concentration of the guest material is increased, the energy transfer speed of the Dexter mechanism also becomes faster, which leads to a decrease in the luminescence efficiency. Therefore, it is difficult to increase the concentration of the guest material. There is a report on the following light-emitting element: in a fluorescent light-emitting element using a material having a function of converting triplet excitation energy into luminescence as a host material, the concentration of the guest material is as low as 1wt% or less.

On the other hand, in a light-emitting element of an embodiment of the present invention, a guest material having a protective group as a light-emitting body is used in the light-emitting layer. Energy transfer based on the Foster mechanism can be efficiently utilized while suppressing energy transfer based on the Dexter mechanism, so the concentration of the guest material as an energy acceptor can be increased. As a result, an originally contradictory phenomenon can be achieved, that is, energy transfer based on the Dexter mechanism is suppressed while increasing the energy transfer rate based on the Foster mechanism. The concentration of the guest material relative to the host material is preferably greater than 2wt% and less than 30wt%, more preferably greater than 5wt% and less than 20wt%, and further preferably greater than 5wt% and less than 15wt%. By adopting this structure, the energy transfer rate based on the Foster mechanism can be increased, so a light-emitting element with high luminescence efficiency can be obtained. Furthermore, by using a material having the function of converting triplet excitation energy into luminescence as a host material, a fluorescent light-emitting element having high luminescence efficiency equivalent to that of a phosphorescent light-emitting element can be manufactured. In addition, since the luminescence efficiency is improved by using a highly stable fluorescent material, a light-emitting element with high reliability can be manufactured.

In addition, in particular, the effect of the light-emitting element of one embodiment of the present invention is not only the effect of improving reliability caused by the use of highly stable fluorescent materials. The above-mentioned energy transfer often competes with the quenching process caused by the influence of deterioration or impurities. When the quenching rate constant of the quenching process increases with time, the luminescence ratio of the light-emitting element decreases. That is, the brightness of the light-emitting element deteriorates. However, as described above, in one embodiment of the present invention, while suppressing the energy transfer based on the Dexter mechanism, the energy transfer rate based on the Foster mechanism can be made higher than that of the known light-emitting element. Therefore, the influence brought about by the competition with the quenching process can be reduced, and the life of the element can be extended.

Here, the luminescent body refers to an atomic group (skeleton) that is the cause of luminescence in a fluorescent material. The luminescent body generally has a π bond, preferably includes an aromatic ring, and preferably has a condensed aromatic ring or a condensed heteroaromatic ring. In addition, as another aspect, the luminescent body can be considered to be an atomic group (skeleton) containing an aromatic ring having a transition dipole vector on the ring plane.

As the condensed aromatic ring or condensed heteroaromatic ring, there can be cited a phenanthrene skeleton, a diphenylethylene skeleton, an acridone skeleton, a phenanthrene skeleton, a phenanthrene skeleton, etc. In particular, a fluorescent material having a naphthalene skeleton, an anthracene skeleton, a fluorene skeleton, a chrysene skeleton, a triphenyl skeleton, a condensed tetraphenyl skeleton, a pyrene skeleton, a perylene skeleton, a coumarin skeleton, a quinacridone skeleton, and a naphthodibenzofuran skeleton is preferred because of its high fluorescence quantum yield.

The protecting group needs to have a triplet excitation energy level higher than the T1 energy level of the luminescent body and the host material. Therefore, it is better to use a saturated hydrocarbon group. This is because the triplet excitation energy level of the substituent without a π bond is high. In addition, the substituent without a π bond does not have the function of transporting carriers (electrons or holes). Therefore, the saturated hydrocarbon group can almost not affect the excited state or carrier transportability of the host material and make the distance between the luminescent body and the host material longer. Furthermore, in organic compounds containing both a substituent having no π bond and a substituent having π conjugation, frontier orbital domains {HOMO (Highest Occupied Molecular Orbital, also called the highest occupied molecular orbital domain) and LUMO (Lowest Unoccupied Molecular Orbital, also called the lowest unoccupied molecular orbital domain)} are often present on the side of the substituent having π conjugation, and in particular, there are many cases where the luminescent body has a frontier orbital domain. As described later, for energy transfer based on the Dexter mechanism, the overlap of the HOMO of the energy donor and the energy acceptor and the overlap of the LUMO of the energy donor and the energy acceptor are important. Therefore, by using a saturated hydrocarbon group as a protecting group, the distance between the frontier orbital domain of the host material as an energy donor and the frontier orbital domain of the guest material as an energy acceptor can be lengthened, thereby suppressing energy transfer based on the Dexter mechanism.

As a specific example of a protecting group, an alkyl group having 1 to 10 carbon atoms can be cited. Since the distance between the luminescent body and the main material needs to be long, the protecting group is preferably a bulky substituent. In other words, a substituent with large steric hindrance is preferred. Therefore, an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms can be applied. In particular, the alkyl group is preferably a bulky branched alkyl group. In addition, the substituent is a bulky substituent when it contains a quaternary carbon, so it is particularly preferred.

In addition, it is preferred to have five or more protecting groups relative to one luminophore. By adopting this structure, the entire luminophore can be covered by the protecting groups, so the distance between the host material and the luminophore can be appropriately adjusted. Although FIG. 2B shows a case where the luminophore and the protecting groups are directly bonded, it is more preferred that the protecting groups are not directly bonded to the luminophore. For example, the protecting group may also be bonded to the luminophore via a divalent or higher substituent such as an aryl group or an amine group. By bonding the protecting group to the luminophore via the substituent, the distance between the luminophore and the host material can be effectively lengthened. Therefore, when the luminophore and the protecting group are not directly bonded, by having four or more protecting groups relative to one luminophore, energy transfer based on the Dexter mechanism can be effectively suppressed.

In addition, the divalent or higher substituent that bonds the luminescent body and the protective group is preferably a substituent having π conjugation. By adopting this structure, the physical properties of the guest material such as the luminescent color, HOMO energy level, and glass transition point can be adjusted. In addition, the protective group is preferably arranged in a manner that is located on the outermost side when the molecular structure is observed with the luminescent body as the center.

<Examples of fluorescent materials and molecular structures having protective groups> Here, the structure of the fluorescent material N,N'-[(2-tert-butylanthracene)-9,10-diyl]-N,N'-bis(3,5-di-tert-butylphenyl)amine (abbreviated as: 2tBu-mmtBuDPhA2Anth) which can be used in a light-emitting element of one embodiment of the present invention, represented by the following structural formula (102) is shown. In 2tBu-mmtBuDPhA2Anth, the anthracene ring is the luminescent body, and the tert-butyl group (tBu group) is used as a protective group.

In FIG3B , the above-mentioned 2tBu-mmtBuDPhA2Anth is represented by a ball-and-stick model. FIG3B shows the situation when 2tBu-mmtBuDPhA2Anth is viewed from the direction of the arrow in FIG3A (the direction horizontal to the anthracene ring plane). The shaded portion in FIG3B represents the portion directly above the anthracene ring plane as the luminescent body, and it can be confirmed that the portion directly above has a region overlapping with the tBu group as the protecting group. For example, in FIG3B , the atom represented by the arrow (a) is the carbon atom of the tBu group overlapping with the shaded portion, and the atom represented by the arrow (b) is the hydrogen atom of the tBu group overlapping with the shaded portion. That is, in 2tBu-mmtBuDPhA2Anth, the atoms constituting the protective group are located directly above one of the luminescent body surfaces, and the atoms constituting the protective group are also located directly above one of the luminescent body surfaces. By adopting this structure, even when the guest material is dispersed in the host material, the distance between the anthracene ring as the luminescent body and the host material can be made long in the plane direction and the vertical direction of the anthracene ring, thereby suppressing the energy transfer based on the Dexter mechanism.

For example, when the migration related to energy transfer is the migration between HOMO and LUMO, the overlap of the HOMO of the host material and the HOMO of the guest material, and the overlap of the LUMO of the host material and the LUMO of the guest material are important for the energy transfer based on the Dexter mechanism. When the HOMO and LUMO of these two materials overlap, the Dexter mechanism occurs significantly. Therefore, in order to suppress the Dexter mechanism, it is important to suppress the overlap of the HOMO and LUMO of the two materials. That is, it is important to make the distance between the skeleton related to the excited state and the host material long. Here, in fluorescent materials, HOMO and LUMO often have a luminescent body. For example, when the HOMO and LUMO of the guest material diffuse above and below the light-emitting surface (above and below the anthracene ring in 2tBu-mmtBuDPhA2Anth), it is important in the molecular structure that the light-emitting surface is covered by the protecting group above and below.

In addition, in a fused aromatic ring or fused heteroaromatic ring such as a pyrene ring or anthracene ring used as a luminescent body, a transition dipole vector exists on the ring plane. Therefore, in FIG3B , 2tBu-mmtBuDPhA2Anth preferably has a region overlapping with the tBu group as a protecting group on the surface where the transition dipole vector exists, that is, directly on the surface of the anthracene ring. Specifically, at least one of the atoms constituting the multiple protecting groups (tBu groups in FIG3A and FIG3B ) is located directly on one surface of the fused aromatic ring or the fused heteroaromatic ring (the anthracene ring in FIG3A and FIG3B ), and at least one of the atoms constituting the multiple protecting groups is located directly on another surface of the fused aromatic ring or the fused heteroaromatic ring. By adopting this structure, even when the guest material is dispersed in the host material, the distance between the light-emitting body and the host material can be made long, thereby suppressing energy transfer based on the Dexter mechanism. In addition, it is preferable to arrange the tBu group so as to cover the light-emitting body such as anthracene ring.

<Reasons for using phosphorescent materials with a five-membered ring skeleton> Next, consider the energy donor. The inventors of this case found that by using a material with a five-membered ring skeleton as a phosphorescent material used as an energy donor, energy transfer based on the Förster mechanism can be effectively utilized. As described later, phosphorescent materials with a five-membered ring skeleton can be appropriately used as a large energy donor.

As the five-membered ring skeleton, it is preferred to use an aromatic ring skeleton, for example, a pyrrole skeleton, a pyrazole skeleton, an imidazole skeleton, a triazole skeleton or a tetrazole skeleton, a benzimidazole skeleton, a naphthylimidazole skeleton, etc. In particular, it is preferred to use a phosphorescent material having an imidazole skeleton, a triazole skeleton, a benzimidazole skeleton, or a naphthylimidazole skeleton, and it is particularly preferred to use a metal complex using the skeleton as a ligand, and it is preferred to include the skeleton as a ligand and have a metal (Ru, Rh, Pd, Os, Ir, or Pt) of the 8th to 10th group and the 5th and 6th period as a central metal, and Ir complexes are particularly preferred. In addition, a benzimidazole skeleton and a naphthylimidazole skeleton are examples of a skeleton having an imidazole skeleton.

Phosphorescent materials having a five-membered ring skeleton as a ligand tend to have a high HOMO energy level. In the light-emitting layer 130, when a material having a high HOMO energy level is used for the above-mentioned compound 133 (energy donor), it is possible to suppress the filling of charge holes in the compound 132 as the guest material (energy acceptor) when a current is passed through the light-emitting element 150. In other words, it is possible to suppress the compound 132 from being positively charged. Except for the above-mentioned excited state complex, the excitation of the compound caused by the current occurs due to the filling of charge holes and electrons on the same molecule. Therefore, by using a material having a high HOMO energy level for compound 133, the current excitation on compound 132 (direct excitation of compound 132) can be suppressed. When compound 132 is directly excited, since compound 132 is a fluorescent material, the triplet excitons generated do not contribute to luminescence, resulting in a decrease in luminescence efficiency. Thus, when the HOMO energy level of the phosphorescent material having a five-membered ring skeleton is high, by using the phosphorescent material as the compound 133, a decrease in the light emission efficiency of the light-emitting element 150 can be suppressed.

<Phosphorescent material with a five-membered ring skeleton as a large energy donor> Here, as a phosphorescent material with a five-membered ring skeleton in a ligand that can be used in one embodiment of the present invention, an example of an Ir complex with a five-membered ring skeleton in a ligand is shown below. Ir(mpptz-diPrp) ₃ is an Ir complex with a triazole skeleton as a five-membered ring skeleton, and fac-Ir(pbi-diBup) ₃ is an Ir complex with an imidazole skeleton.

As in the above-mentioned Ir complex, when a five-membered ring skeleton having two or more nitrogen atoms in the five-membered ring skeleton, such as an imidazole skeleton or a triazole skeleton, is used as the five-membered ring skeleton possessed by the ligand, there is nitrogen that is not coordinated with the metal. At least one of the nitrogen that is not coordinated with the metal is not related to the double bond, so the aromatic ring can be maintained and a substituent (a nitrogen atom surrounded by a circle in the above-mentioned Ir complex) can be included. As the substituent, various substituents such as hydrogen, alkyl, and aromatic hydrocarbon groups can be cited, and it is preferred to use a substituted or unsubstituted aromatic hydrocarbon group with 6 to 13 carbon atoms. In particular, it is preferred to use an unsubstituted phenyl group or a phenyl group having one or more alkyl groups with 1 to 6 carbon atoms. In addition, the phenyl group may also be bonded with an electron-withdrawing group such as fluorine, cyano, or fluorinated alkyl. By adopting this structure, the thermal stability and sublimation properties of the Ir complex can be improved.

Therefore, when a compound having a five-membered ring skeleton is used as a ligand of an Ir complex, the nitrogen atom preferably has a substituted or unsubstituted aromatic hydrocarbon group having 6 to 13 carbon atoms as a substituent. By having the substituent, the ligand has a bulky structure with large steric hindrance. As a result, the Ir complex has a bulky structure. In other words, when a compound having a five-membered ring skeleton is used as a ligand of a phosphorescent material, the Ir complex tends to have a bulky structure.

Here, let's consider the case where the Ir complex is excited. In the Ir complex of the phosphorescent material, the lowest triplet excitation energy level often originates from the triplet MLCT. Therefore, the triplet excitation energy often exists near the Ir atom and the part of the ligand coordinated to the Ir atom (nitrogen atom coordinated to Ir, or adjacent metallized carbon atom).

Here, we consider the case where an Ir complex having a bulky ligand is dispersed in the light-emitting layer. The bulky ligand can increase the distance between the Ir atoms in the Ir complex and the material surrounding the Ir complex. In other words, the deactivation of triplet excitation energy based on the Dexter mechanism can be suppressed.

Here, the case where this large Ir complex is used for the above-mentioned compound 133 is considered. As described above, the deactivation of the excitation energy from compound 133 to compound 132 based on the Dexter mechanism (path A ₃ ) can be suppressed. Therefore, the energy transfer via the path A ₂ (energy transfer based on the Förster mechanism) can be efficiently utilized. In this way, by using an Ir complex having a five-membered ring skeleton as a ligand, a light-emitting element with high light-emitting efficiency can be obtained.

In addition, as described above, by using an Ir complex having a five-membered ring skeleton as a ligand as an energy donor, the transfer of excitation energy based on the Dexter mechanism can be suppressed. Therefore, when an Ir complex having a five-membered ring as a ligand is used as an energy donor, even if the number of protecting groups possessed by the energy acceptor as the guest material is small, the energy transfer via the path _A2 can be efficiently utilized. In this case, the energy acceptor preferably has at least two protecting groups for each luminescent body, more preferably has three or more protecting groups, and further preferably has four or more protecting groups. As a five-membered ring skeleton of the ligand used for the Ir complex, an imidazole skeleton or a triazole skeleton is preferably used. Furthermore, in the Ir complex, it is more preferred to adopt a structure in which a substituted or unsubstituted aromatic hydrocarbon group having 6 to 13 carbon atoms is bonded to a nitrogen atom which is not bonded to Ir and is not involved in a double bond. In addition, when the aromatic hydrocarbon group is a phenyl group and the phenyl group has a substituent, the substituent is more preferably an alkyl group having 1 to 6 carbon atoms.

Specifically, as the aromatic group having 6 to 13 carbon atoms, there can be mentioned phenyl, biphenyl, naphthyl, fluorenyl, etc. Also, as the alkyl group having 1 to 6 carbon atoms, there can be mentioned methyl, ethyl, propyl, pentyl, hexyl, cyclohexyl, norbornyl, adamantyl, isopropyl, dibutyl, isobutyl, tertiary butyl, isopentyl, dipentyl, tertiary pentyl, neopentyl, isohexyl, 3-methylpentyl, 2-methylpentyl, 2-ethylbutyl, 1,2-dimethylbutyl, 2,3-dimethylbutyl, etc. Note that the aromatic group having 6 to 13 carbon atoms and the alkyl group having 1 to 6 carbon atoms are not limited thereto.

In addition, the triplet excitation energy of an Ir complex having a five-membered ring skeleton as a ligand is higher than that of an Ir complex consisting of only a six-membered ring skeleton. Therefore, when a fluorescent material emitting shorter wavelengths such as green and blue is used as an energy acceptor as Compound 132, an Ir complex having a five-membered ring skeleton as a ligand is preferably used as an energy donor.

As described later, in the energy transfer based on the Förster mechanism, the greater the overlap between the absorption spectrum of the energy acceptor (absorption band on the longest wavelength side (absorption band mainly derived from the S1 energy level)) and the emission spectrum of the energy donor, the better. When a fluorescent material has a luminescence peak on the shorter wavelength side (400nm to 580nm) from blue to green, the absorption band of the fluorescent material may also exist on the short wavelength side. Therefore, in order to expand the overlap between the absorption band and the emission spectrum of the energy donor, it is preferred to use an energy donor with a large triplet excitation energy.

In addition, by using a phosphorescent material having a five-membered ring skeleton in compound 133, energy transfer based on the Förster mechanism can be efficiently utilized while suppressing energy transfer based on the Dexter mechanism. Therefore, when compound 133 as an energy donor is added to the light-emitting layer 130, its concentration can be increased. As a result, a phenomenon that is originally contradictory can be achieved, that is, energy transfer based on the Dexter mechanism is suppressed while increasing the energy transfer rate based on the Förster mechanism. The concentration of compound 133 relative to the host material is preferably greater than 2wt% and less than 30wt%, more preferably greater than 5wt% and less than 20wt%, and further preferably greater than 5wt% and less than 15wt%. By adopting this structure, the energy transfer rate based on the Förster mechanism can be increased, so a light-emitting element with high light-emitting efficiency can be obtained. In addition, since the luminescence efficiency is improved by using a highly stable fluorescent material, a highly reliable light-emitting element can be manufactured. Note that the concentrations of compound 133 and compound 132 of the fluorescent material are preferably both high. In addition, the concentrations of compound 133 and compound 132 are preferably about the same high. Specifically, the concentration ratio of compound 133 to compound 132 is preferably 1:0.2 or more and 1:5 or less, and more preferably 1:0.5 or more and 1:2 or less.

<Structural example 2 of the light-emitting layer> Figure 4C shows an example of the energy level correlation in the light-emitting layer 130 of the light-emitting element 150 of one embodiment of the present invention. The light-emitting layer 130 shown in Figure 4A includes compound 131, compound 132, and compound 133. In one embodiment of the present invention, compound 132 is preferably a fluorescent material. In addition, in this structural example, compound 131 and compound 133 are a combination that forms an excited state complex. The following describes the case where compound 133 is a phosphorescent material having a five-membered ring skeleton.

As a combination of compound 131 and compound 133, any combination that can form an excited complex is sufficient, and preferably one of them is a compound having a function of transporting holes (hole transportability) and the other is a compound having a function of transporting electrons (electron transportability). In this case, a donor-acceptor type excited complex is easily formed, and an excited complex can be formed efficiently. In addition, when the combination of compound 131 and compound 133 is a combination of a compound having hole transportability and a compound having electron transportability, the balance of carriers can be easily controlled by adjusting their mixing ratio. Specifically, the ratio of compound having hole transportability:compound having electron transportability is preferably in the range of 1:9 to 9:1 (weight ratio). In addition, by having this structure, the balance of carriers can be easily controlled, thereby also making it easy to control the carrier recombination region. The HOMO level of phosphorescent materials having a five-membered ring skeleton is easily increased, and therefore, they are preferably used as materials having hole transport properties.

In addition, as a combination of host materials that efficiently forms an excited complex, it is preferred that the HOMO energy level of one of Compound 131 and Compound 133 is higher than the HOMO energy level of the other, and the LUMO energy level of one of them is higher than the LUMO energy level of the other. In addition, the HOMO energy level of Compound 131 may be equal to the HOMO energy level of Compound 133, or the LUMO energy level of Compound 131 may be equal to the LUMO energy level of Compound 133.

Note that the LUMO energy level and the HOMO energy level of a compound can be obtained from the electrochemical properties (reduction potential and oxidation potential) of the compound measured by cyclic voltammetry (CV) measurement.

For example, when compound 133 has hole transportability and compound 131 has electron transportability, as shown in the energy band diagram of FIG4B , it is preferred that the HOMO energy level of compound 133 is higher than the HOMO energy level of compound 131, and the LUMO energy level of compound 133 is higher than the LUMO energy level of compound 131. Due to this energy level correlation, holes and electrons as carriers injected from a pair of electrodes (electrode 101 and electrode 102) are easily injected into compound 133 and compound 131, respectively, which is preferred.

In addition, in Figure 4B, Comp(131) represents compound 131, Comp(133) represents compound 133, ∆E _C1 represents the energy difference between the LUMO energy level and the HOMO energy level of compound 131, ∆E _C3 represents the energy difference between the LUMO energy level and the HOMO energy level of compound 133, and ∆E _E represents the energy difference between the LUMO energy level of compound 131 and the HOMO energy level of compound 133.

In addition, the excited complex formed by Compound 131 and Compound 133 has a molecular orbital of HOMO in Compound 133 and a molecular orbital of LUMO in Compound 131. In addition, the excitation energy of the excited complex is approximately equivalent to the energy difference (∆E _E ) between the LUMO energy level of Compound 131 and the HOMO energy level of Compound 133, and is smaller than the energy difference (∆E _C1 ) between the LUMO energy level and the HOMO energy level of Compound 131 and the energy difference (∆E _C3 ) between the LUMO energy level and the HOMO energy level of Compound 133. Therefore, by forming an excited complex by Compound 131 and Compound 133, an excited state can be formed with a lower excitation energy. In addition, the excited complex can form a stable excited state due to its lower excitation energy.

FIG4C shows the energy level correlation of compound 131, compound 132, and compound 133 in the light-emitting layer 130. The following are the notations and symbols in FIG4C. • Comp(131): compound 131 • Comp(133): compound 133 • Guest(132): compound 132 • S _C1 : S1 energy level of compound 131 • T _C1 : T1 energy level of compound 131 • S _C3 : S1 energy level of compound 133 • T _C3 : S1 energy level of compound 133 • S _G : S1 energy level of compound 132 • T _G : T1 energy level of compound 132 • S _E : S1 energy level of excited complex • T _E : T1 energy level of excited complex

In the light-emitting device of one embodiment of the present invention, the compound 131 and the compound 133 included in the light-emitting layer 130 form an excited complex. The S1 energy level ( _SE ) of the excited complex and the T1 energy level ( _TE ) of the excited complex are adjacent energy levels (see path _A4 in FIG4C).

The excitation energy levels ( _SE and _TE ) of the excited complex are lower than the S1 energy levels ( _SC1 and _SC3 ) of the substances forming the excited complex (Compound 131 and Compound 133), so an excited state can be formed with lower excitation energy. Thus, the driving voltage of the light-emitting element 150 can be reduced.

Because the S1 energy level ( _SE ) and T1 energy level ( _TE ) of the excited complex are adjacent energy levels, antisystem crossing is easily generated and TADF characteristics are obtained. Therefore, the excited complex has the function of converting triplet excitation energy into singlet excitation energy by up-conversion (path _A5 in Figure 4C). The singlet excitation energy of the excited complex can be quickly transferred to compound 132 (path _A6 in Figure 4C). At this time, it is preferred to satisfy _SE ≥ _SG . In path _A6 , the excited complex is used as an energy donor and compound 132 is used as an energy acceptor. Specifically, it is preferred that a tangent line is drawn at the tail of the short-wavelength side of the fluorescence spectrum of the excited complex, and the energy of the wavelength of its extrapolated line is set to _SE , and the energy of the wavelength of the absorption end of the absorption spectrum of compound 132 or the tail of the short-wavelength side of the fluorescence spectrum of compound 132 is drawn, and the energy of the wavelength of its extrapolated line is set to _SG , in which case _SE ≥ _SG is satisfied.

In order to improve the TADF characteristics, it is preferred that the T1 energy level of Compound 131 and Compound 133, that is, T _C1 and T _C3 , be greater than _TE . As an indicator thereof, it is preferred that the emission peak wavelength on the shortest wavelength side of the phosphorescence spectrum of Compound 131 and Compound 133 is less than the maximum emission peak wavelength of the excited complex. Alternatively, it is preferred that a tangent line is drawn at the tail of the emission spectrum of the excited complex on the short-wavelength side, and the energy of the wavelength of the extrapolated line is set to _TE , and tangent lines are drawn at the tail of the phosphorescence spectra of compound 131 and compound 133 on the short-wavelength side, and the energy of the wavelength of the extrapolated line is set to _TC1 and _TC3 of each compound, in which case _TE - _TC1 ≤0.2 eV and _TE - _TC3 ≤0.2 eV are preferred.

In addition, in this structural example, a compound containing a heavy atom is used as one of the compounds that form an excited complex. Therefore, the intersystem transition between the singlet excited state and the triplet excited state is promoted. Therefore, an excited complex that can convert triplet excitation energy into luminescence can be formed. At this time, unlike a general excited complex, the triplet excitation energy level ( _TE ) of the excited complex may be the energy level of an energy donor, so _TE is preferably higher than the singlet excitation energy level ( _SG ) of compound 132 as a luminescent material. Specifically, it is preferred that a tangent line is drawn at the tail of the emission spectrum of the excited complex using a heavy atom on the short wavelength side, the energy of the wavelength of the extrapolated line is set to _TE , and the energy of the wavelength of the absorption end of the absorption spectrum of compound 132 or the tail of the emission spectrum of compound 132 on the short wavelength side is drawn, and the energy of the wavelength of the extrapolated line is set to _SG , in which case _TE ≥ _SG is satisfied.

In the case of such energy level correlation, the triplet excitation energy of the generated excited complex can be transferred from the triplet excitation energy level ( _TE ) of the excited complex directly or via the singlet excitation energy level ( _SE ) to the singlet excitation energy level ( _SG ) of compound 132. Note that the S1 energy level ( _SE ) and the T1 energy level ( _TE ) of the excited complex are adjacent to each other, so that it is sometimes difficult to clearly distinguish between fluorescence and phosphorescence in the emission spectrum. In this case, fluorescence and phosphorescence can sometimes be distinguished based on the luminescence lifetime.

The triplet excitation energy generated in the light-emitting layer 130 passes through the above-mentioned path _A4 and the energy transfer from the S1 energy level of the excited state complex to the S1 energy level of the guest material (path _A6 ), thereby making the guest material emit light. Therefore, by using the combination of materials that form the excited state complex for the light-emitting layer 130, the light-emitting efficiency of the fluorescent light-emitting element can be improved.

The compound with heavy atoms used in the above structure preferably contains heavy atoms such as Ir, Pt, Os, Ru, Pd, etc. In addition, the compound with heavy atoms is preferably a phosphorescent material. On the other hand, in the present structural example, the phosphorescent material is a material constituting an excited complex used as an energy donor, so its quantum yield can be either high or low. That is, the energy transfer from the triplet excitation energy level of the excited complex to the singlet excitation energy level of the guest material directly or via the singlet excitation energy level is an allowed transition. In the energy transfer from the excited complex composed of the above phosphorescent material or the above phosphorescent material to the guest material, the energy transfer from the triplet excitation energy level of the energy donor to the singlet excitation energy level of the guest material (energy acceptor) is an allowed transition, so it is preferred. Therefore, there is a path for transferring the triplet excitation energy of the excited complex to the S1 energy level ( _SG ) of the guest material via the path _A6 without going through the path _A5 in Figure 4C. In the path _A6 , the excited complex is used as an energy donor and compound 132 is used as an energy acceptor.

Here, in a light-emitting element of one embodiment of the present invention, a guest material whose light-emitting body has a protective group is used for compound 132. By adopting this structure, as described above, energy transfer based on the Dexter mechanism represented by path _A7 can be suppressed, and deactivation of triplet excitation energy can be suppressed. Therefore, a fluorescent light-emitting element with high light-emitting efficiency can be obtained.

In one embodiment of the present invention, a phosphorescent material having a five-membered ring skeleton is used. By adopting this structure, as described above, the energy transfer based on the Dexter mechanism represented by the path _A7 can be suppressed, and the deactivation of the triplet excitation energy can be suppressed. In addition, the recombination in the compound 132 can be suppressed. Therefore, a fluorescent light-emitting element with high light-emitting efficiency can be obtained.

In this specification, the process of the above-mentioned path _A4 to _A6 is sometimes referred to as ExSET (Exciplex-Singlet Energy Transfer) or ExEF (Exciplex-Enhanced Fluorescence). In other words, in the light-emitting layer 130, the excitation energy is supplied from the exciplex to the fluorescent material.

<Structural example 3 of the light-emitting layer> Figure 5A shows the case where four materials are used for the light-emitting layer 130. The light-emitting layer 130 in Figure 5A includes compound 131, compound 132, compound 133, and compound 134. In one embodiment of the present invention, compound 133 has a function of converting triplet excitation energy into luminescence. In this structural example, the explanation is based on the premise that compound 133 is a phosphorescent material having a five-membered ring skeleton. Compound 132 is a guest material that exhibits fluorescent luminescence. In addition, compound 131 is an organic compound that forms an excited complex with compound 134.

In addition, FIG5B shows the energy level correlation of compound 131, compound 132, compound 133, and compound 134 in the light-emitting layer 130. The following are the symbols and signs in FIG5B, and the other symbols and signs are the same as those shown in FIG2B. • S _C4 : S1 energy level of compound 134 • T _C4 : T1 energy level of compound 134

In the light-emitting device of one embodiment of the present invention shown in this structural example, the compound 131 and the compound 134 contained in the light-emitting layer 130 form an excited complex. The S1 energy level ( _SE ) of the excited complex and the T1 energy level ( _TE ) of the excited complex are adjacent energy levels (see path _A8 in FIG5B).

The excited complex generated by the above process is as described above, and when the excitation energy is lost, the two substances forming the excited complex are used again as the original two substances.

The excitation energy levels ( _SE and _TE ) of the excited complex are lower than the S1 energy levels ( _SC1 and _SC4 ) of the substances forming the excited complex (Compound 131 and Compound 134), so an excited state can be formed with lower excitation energy. Thus, the driving voltage of the light-emitting element 150 can be reduced.

Here, when compound 133 is a phosphorescent material, intersystem crossing between a singlet excited state and a triplet excited state is allowed. Therefore, both the singlet excitation energy and the triplet excitation energy of the excited complex can be quickly transferred to compound 133 (path A ₉ ). Here, it is preferred to satisfy _TE ≥ _TC3 . In addition, the triplet excitation energy possessed by compound 133 can be efficiently converted into the singlet excitation energy of compound 132 (path A ₁₀ ). Here, as shown in FIG. 5B , in the case of _TE ≥ _TC3 ≥ _SG , the excitation energy of compound 133 is efficiently transferred as singlet excitation energy to compound 132 as a guest material, so it is preferred. Specifically, it is preferred that a tangent line is drawn at the tail of the short-wavelength side of the phosphorescence spectrum of compound 133, and the energy of the wavelength of its extrapolation line is set to _TC3 , and the energy of the wavelength of the absorption end of the absorption spectrum of compound 132 or the tail of the short-wavelength side of the fluorescence spectrum of compound 132 is drawn at the tail, and the energy of the wavelength of its extrapolation line is set to _SG , and then _TC3 ≥ _SG is satisfied. In path A ₁₀ , compound 133 is used as an energy donor, and compound 132 is used as an energy acceptor.

In this case, the combination of Compound 131 and Compound 134 may be any combination as long as it can form an exciplex, and preferably one of them is a compound having a hole transport property and the other is a compound having an electron transport property.

In addition, as a combination of materials that efficiently forms an exciplex, it is preferred that the HOMO energy level of one of Compound 131 and Compound 134 is higher than the HOMO energy level of the other, and the LUMO energy level of one of Compound 131 and Compound 134 is higher than the LUMO energy level of the other.

In addition, the energy level correlation between compound 131 and compound 134 is not limited to the energy level correlation shown in Figure 5B. That is, the singlet excitation energy level (S _C1 ) of compound 131 may be higher than the singlet excitation energy level (S _C4 ) of compound 134 or lower than the singlet excitation energy level (S _C4 ) of compound 134. In addition, the triplet excitation energy level (T _C1 ) of compound 131 may be higher than the triplet excitation energy level (T _C4 ) of compound 134 or lower than the triplet excitation energy level (T _C4 ) of compound 134.

In the light-emitting device of one embodiment of the present invention, the compound 131 preferably has a π-electron-deficient skeleton. By adopting this structure, the LUMO energy level of the compound 131 becomes lower, which is suitable for the formation of an excited complex.

In the light-emitting device of one embodiment of the present invention, the compound 131 preferably has a π-electron-rich skeleton. By adopting this structure, the HOMO energy level of the compound 131 becomes higher, which is suitable for the formation of an excited complex.

Here, in a light-emitting element of one embodiment of the present invention, a guest material whose light-emitting body has a protective group is used for compound 132. By adopting this structure, as described above, energy transfer based on the Dexter mechanism represented by path A ₁₁ can be suppressed, and deactivation of triplet excitation energy can be suppressed. Therefore, a fluorescent light-emitting element with high light-emitting efficiency can be obtained.

In one embodiment of the present invention, a phosphorescent material having a five-membered ring skeleton is used for compound 133. By adopting this structure, as described above, energy transfer based on the Dexter mechanism represented by path _A11 can be suppressed, and deactivation of triplet excitation energy can be suppressed. In addition, recombination of carriers in compound 132 can be suppressed. Therefore, a fluorescent light-emitting element with high light-emitting efficiency can be obtained.

In this specification, etc., the process of the above-mentioned paths _A8 and _A9 is sometimes referred to as ExTET (Exciplex-Triplet Energy Transfer). In other words, in the light-emitting layer 130, the excitation energy is supplied from the excited complex to the compound 133. Therefore, it can be said that this structural example is a structure in which a fluorescent material having a protective group is mixed into a light-emitting layer that can use ExTET.

<Structural Example 4 of Light Emitting Layer> In this structural example, a case where a material having TADF characteristics is used for the compound 134 described in the structural example 3 of the light emitting layer described above is described.

FIG5C shows a case where four materials are used for the light-emitting layer 130. The light-emitting layer 130 in FIG5C includes compound 131, compound 132, compound 133, and compound 134. In one embodiment of the present invention, compound 133 has a function of converting triplet excitation energy into luminescence. Compound 132 is a guest material exhibiting fluorescent luminescence. In addition, compound 131 is an organic compound that forms an excited state complex with compound 134. In addition, in this structural example, a case where compound 133 has a phosphorescent material with a five-membered ring skeleton is described.

Here, since compound 134 is a TADF material, compound 134 without forming an excited complex has the function of converting triplet excitation energy into singlet excitation energy by up-conversion (path A ₁₂ in FIG. 5C ). The singlet excitation energy of compound 134 can be quickly transferred to compound 132 (path A ₁₃ in FIG. 5C ). At this time, it is preferred to satisfy _SC4 ≥ _SG . Specifically, it is preferred that a tangent line is drawn at the tail of the short-wavelength side of the fluorescence spectrum of compound 134, and the energy of the wavelength of its extrapolated line is set to _SC4 , and the energy of the wavelength of the absorption end of the absorption spectrum of compound 132 or the tail of the short-wavelength side of the fluorescence spectrum of compound 132 is drawn, and the energy of the wavelength of its extrapolated line is set to _SG , in which case _SC4 ≥ _SG is satisfied.

Similar to the structural example of the light-emitting layer, in the light-emitting element of one embodiment of the present invention, there are paths for triplet excitation energy to be transferred to compound 132 as a guest material via paths _A8 to _A10 in FIG. 5B , and paths for triplet excitation energy to be transferred to compound 132 via paths _A12 and _A13 in FIG. 5C . Since there are multiple paths for triplet excitation energy to be transferred to the fluorescent material, the light-emitting efficiency can be further improved. In path _A10 , compound 133 is used as an energy donor, and compound 132 is used as an energy acceptor. In path _A13 , compound 134 is used as an energy donor, and compound 132 is used as an energy acceptor.

Here, in one embodiment of the present invention, a guest material whose luminescent body has a protecting group is used for compound 132. By adopting this structure, as described above, energy transfer based on the Dexter mechanism represented by path A ₁₁ can be suppressed, and deactivation of triplet excitation energy can be suppressed. Therefore, a fluorescent light-emitting element with high luminescence efficiency can be obtained.

In addition, in a light-emitting element of an embodiment of the present invention, a phosphorescent material whose light-emitting body has a five-membered ring skeleton is used for compound 133. By adopting this structure, as described above, energy transfer based on the Dexter mechanism represented by path A ₁₁ can be suppressed, and deactivation of triplet excitation energy can be suppressed. In addition, recombination of carriers in compound 132 can be suppressed. Therefore, a fluorescent light-emitting element with high light-emitting efficiency can be obtained.

<Energy transfer mechanism> The following describes the Foster mechanism and the Dexter mechanism. Although the energy transfer process between the molecules of the first material and the second material is described here in terms of the supply of excitation energy from the first material in an excited state to the second material in a ground state, the same is true when either of the above is an excited complex.

<<Foster mechanism>> In the Foster mechanism, direct contact between molecules is not required for energy transfer, and energy transfer occurs through the resonance phenomenon of dipole oscillation between the first material and the second material. Through the resonance phenomenon of dipole oscillation, the first material supplies energy to the second material, and the excited state of the first material becomes the ground state, and the ground state of the second material becomes the excited state. In addition, the rate constant k _{h* → g} of the Foster mechanism is shown in formula (1).

In formula (1), ν represents the oscillation number, _f'h (ν) represents the normalized emission spectrum of the first material (fluorescence spectrum when discussing energy transfer from a singlet excited state, and phosphorescence spectrum when discussing energy transfer from a triplet excited state), _εg (ν) represents the molar absorption coefficient of the second material, N represents the Avogadro number, n represents the refractive index of the medium, R represents the molecular distance between the first material and the second material, τ represents the measured lifetime of the excited state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, φ represents the luminescence quantum yield (fluorescence quantum yield when discussing energy transfer from a singlet excited state, and phosphorescence quantum yield when discussing energy transfer from a triplet excited state), and ^K2 represents the coefficient of the orientation of the transition dipole moments of the first material and the second material (0 to 4). In addition, in the random alignment, K ² =2/3.

＜＜Dexter mechanism＞＞ In the Dexter mechanism, the first material and the second material are close to the contact effective distance that produces the overlap of the orbital domains, and energy transfer occurs by exchanging the electrons of the excited state of the first material and the electrons of the ground state of the second material. In addition, the rate constant k _{h* → g} of the Dexter mechanism is shown in formula (2).

In formula (2), h represents Planck's constant, K represents a constant having an energy dimension, ν represents the oscillation number, f' _h (ν) represents the normalized emission spectrum of the first material (fluorescence spectrum when discussing energy transfer from a singlet excited state, phosphorescence spectrum when discussing energy transfer from a triplet excited state), ε' _g (ν) represents the normalized absorption spectrum of the second material, L represents the effective molecular radius, and R represents the molecular distance between the first material and the second material.

Here, the energy transfer efficiency φ _ET from the first material to the second material is expressed by formula (3). _{k r} represents the rate constant of the luminescence process of the first material (fluorescence when discussing energy transfer from a singlet excited state, phosphorescence when discussing energy transfer from a triplet excited state), k _n represents the rate constant of the non-luminescence process (thermal deactivation or intersystem crossing) of the second material, and τ represents the lifetime of the excited state of the first material being measured.

From formula (3), we can see that in order to improve the energy transfer efficiency φ _ET , we can increase the energy transfer rate constant k _{h* → g} to make other competing rate constants k _r +k _n (=1/τ) relatively smaller.

＜＜Concept for improving energy transfer＞＞ First, consider energy transfer based on the Förster mechanism. By substituting equation (1) into equation (3), τ can be eliminated. Therefore, in the Förster mechanism, the energy transfer efficiency φ _ET does not depend on the lifetime τ of the excited state of the first material. In addition, when the luminescence quantum yield φ is high, it can be said that the energy transfer efficiency φ _ET is high.

In addition, the overlap between the emission spectrum of the first material and the absorption spectrum of the second material (equivalent to the absorption of the transition from the singlet ground state to the singlet excited state) is preferably large. Furthermore, the molar absorption coefficient of the second material is preferably high. This means that the emission spectrum of the first material overlaps with the absorption band that appears on the longest wavelength side of the second material. Note that since the direct transition from the singlet ground state to the triplet excited state is prohibited in the second material, the molar absorption coefficient in the triplet excited state is so small that it can be ignored in the second material. Therefore, the energy transfer process from the excited state of the first material to the triplet excited state of the second material based on the Förster mechanism can be ignored, and only the energy transfer process to the singlet excited state of the second material needs to be considered.

In addition, according to formula (1), the energy transfer rate based on the Förster mechanism is inversely proportional to the sixth power of the molecular distance R between the first material and the second material. As described above, when R is less than 1 nm, the energy transfer based on the Dexter mechanism is dominant. Therefore, in order to suppress the energy transfer based on the Dexter mechanism while increasing the energy transfer rate based on the Förster mechanism, the molecular distance is preferably greater than 1 nm and less than 10 nm. Therefore, the above-mentioned protecting group is required not to be too large, and the number of carbon atoms constituting the protecting group is preferably greater than 3 and less than 10.

Next, consider the energy transfer based on the Dexter mechanism. From formula (2), it can be seen that in order to increase the rate constant k _{h* → g} , the emission spectrum of the first material (the fluorescence spectrum when discussing the energy transfer from the singlet excited state, the phosphorescence spectrum when discussing the energy transfer from the triplet excited state) and the absorption spectrum of the second material (equivalent to the absorption of the transition from the singlet ground state to the singlet excited state) should preferably overlap more. Therefore, the energy transfer efficiency can be optimized by overlapping the emission spectrum of the first material with the absorption band on the longest wavelength side of the second material.

In addition, when formula (2) is substituted into formula (3), it can be seen that the energy transfer efficiency φ _ET in the Dexter mechanism depends on τ. Since the Dexter mechanism is an energy transfer process based on electron exchange, energy transfer from the triplet excited state of the first material to the triplet excited state of the second material also occurs in the same manner as energy transfer from the singlet excited state of the first material to the triplet excited state of the second material.

In a light-emitting element of an embodiment of the present invention, the second material is a fluorescent material, so the energy transfer efficiency of the triplet excited state to the second material is preferably low. In other words, the energy transfer efficiency based on the Dexter mechanism from the first material to the second material is preferably low, and the energy transfer efficiency based on the Foster mechanism from the first material to the second material is preferably high.

As described above, the energy transfer efficiency based on the Foster mechanism does not depend on the lifetime τ of the excited state of the first material. On the other hand, the energy transfer efficiency based on the Dexter mechanism depends on the excitation lifetime τ of the first material. In order to reduce the energy transfer efficiency based on the Dexter mechanism, the excitation lifetime τ of the first material is preferably short.

Therefore, in one embodiment of the present invention, an excited state complex, a phosphorescent material or a TADF material is used as the first material. These materials have the function of converting triplet excitation energy into luminescence. The energy transfer efficiency of the Förster mechanism depends on the luminescence quantum yield of the energy donor. Therefore, the first material such as the phosphorescent material, excited state complex or TADF material that can convert the triplet excited state into luminescence can utilize the Förster mechanism to transfer its excitation energy to the second material. On the other hand, by means of the structure of one embodiment of the present invention, the antisystem transition from the triplet excited state to the singlet excited state of the first material (excited state complex or TADF material) can be promoted, and the excitation lifetime τ of the triplet excited state of the first material can be shortened. In addition, the transition from the triplet excited state to the singlet ground state of the first material (phosphorescent material or excited complex using the phosphorescent material) can be promoted, and the excitation lifetime τ of the triplet excited state of the first material can be shortened. As a result, the energy transfer efficiency based on the Dexter mechanism from the triplet excited state of the first material to the triplet excited state of the fluorescent material (second material) can be reduced.

In a light-emitting element of an embodiment of the present invention, as described above, a fluorescent material having a protective group is used as the second material. Therefore, the molecular distance between the first material and the second material can be made large. Therefore, in a light-emitting element of an embodiment of the present invention, by using a material having a function of converting triplet excitation energy into luminescence as the first material and using a fluorescent material having a protective group as the second material, the energy transfer efficiency based on the Dexter mechanism can be reduced. As a result, the radiationless deactivation of the triplet excitation energy in the light-emitting layer 130 can be suppressed, thereby providing a light-emitting element with high luminescence efficiency.

<Materials> Next, the components of a light-emitting element according to one embodiment of the present invention are described.

<<Luminescent layer>> The following describes the materials that can be used for the luminescent layer 130. In the luminescent layer of the luminescent element of one embodiment of the present invention, an energy acceptor having a function of converting triplet excitation energy into luminescence and an energy donor having a protective group in the luminescent body are used. As materials having a function of converting triplet excitation energy into luminescence, TADF characteristic materials and phosphorescent materials can be cited.

Examples of the luminescent material of compound 132 used as an energy acceptor include a phenanthrene skeleton, a diphenylethylene skeleton, an acridone skeleton, a phenanthrene skeleton, a phenanthrene skeleton, and a phenanthrenethio skeleton. In particular, fluorescent materials having a naphthalene skeleton, anthracene skeleton, fluorene skeleton, chrysene skeleton, a triphenylene skeleton, a tetraphenylene skeleton, a pyrene skeleton, a perylene skeleton, a coumarin skeleton, a quinacridone skeleton, and a naphthodibenzofuran skeleton are preferred because they have a high fluorescence quantum yield.

In addition, the protecting group is preferably an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a branched alkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 12 carbon atoms.

Examples of the alkyl group having 1 to 10 carbon atoms include methyl, ethyl, propyl, pentyl, and hexyl groups, and particularly preferred are branched alkyl groups having 3 to 10 carbon atoms described below. Note that the alkyl group is not limited thereto.

As the cycloalkyl group having 3 or more and 10 or less carbon atoms, cyclopropyl, cyclobutyl, cyclohexyl, norbornyl, adamantyl, etc. can be mentioned. The cycloalkyl group is not limited thereto. In addition, when the cycloalkyl group has a substituent, as the substituent, alkyl groups having 1 to 7 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, dibutyl, tertiary butyl, pentyl and hexyl, cycloalkyl groups having 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, cycloheptyl and 8,9,10-trinorbornyl, and aryl groups having 6 to 12 carbon atoms such as phenyl, naphthyl and biphenyl can be mentioned.

Examples of the branched alkyl group having 3 to 10 carbon atoms include isopropyl, dibutyl, isobutyl, tertiary butyl, isopentyl, dipentyl, tertiary pentyl, neopentyl, isohexyl, 3-methylpentyl, 2-methylpentyl, 2-ethylbutyl, 1,2-dimethylbutyl, and 2,3-dimethylbutyl. The branched alkyl group is not limited thereto.

Examples of the trialkylsilyl group having 3 to 12 carbon atoms include trimethylsilyl, triethylsilyl, tertiary butyldimethylsilyl, etc. The trialkylsilyl group is not limited thereto.

In addition, as the molecular structure of the energy acceptor, it is preferred that the luminescent body is bonded to two or more diarylamine groups and each aryl group possessed by the diarylamine group has at least one protecting group. It is more preferred that at least two protecting groups are bonded to each aryl group. This is because: the more the number of protecting groups, the greater the effect of suppressing the energy transfer based on the Dexter mechanism when the guest material is used in the luminescent layer. In order to suppress the increase of molecular weight and maintain sublimation, the diarylamine group is preferably a diphenylamine group.

By bonding two or more amine groups to the luminescent body, a fluorescent material with a high quantum yield can be obtained while adjusting the luminescent color. In addition, the amine groups are preferably bonded to positions symmetrical with respect to the luminescent body. By adopting this structure, a fluorescent material with a high quantum yield can be realized.

In addition, the protecting group may be bonded to the luminescent body via the aryl group of the diarylamine, rather than directly bonding the protecting group to the luminescent body. By adopting this structure, the protecting group can be arranged in a manner covering the luminescent body, so the distance between the main material and the luminescent body can be made long from all directions, which is preferred. In addition, when the protecting group is not directly bonded to the luminescent body, it is preferred to bond four or more protecting groups to one luminescent body.

In addition, as shown in FIG3B , it is preferred that at least one of the atoms constituting the plurality of protecting groups is located directly on the luminescent body, that is, directly on one face of the fused aromatic ring or the fused heteroaromatic ring, and at least one of the atoms constituting the plurality of protecting groups is located directly on another face of the fused aromatic ring or the fused heteroaromatic ring. As a specific method, the following structure can be cited. That is, the fused aromatic ring or the fused heteroaromatic ring of the luminescent body is bonded to two or more diphenylamine groups, and the phenyl groups in the two or more diphenylamine groups have protecting groups at the 3-position and the 5-position, respectively, independently.

By adopting such a structure, as shown in FIG3B , a configuration can be achieved in which the protecting group at the 3-position or 5-position on the phenyl group is located directly above the condensed aromatic ring or condensed heteroaromatic ring that is the luminescent body. As a result, the upper and lower surfaces of the condensed aromatic ring or the condensed heteroaromatic ring can be efficiently covered, and energy transfer based on the Dexter mechanism can be suppressed.

As the energy acceptor material as described above, an organic compound represented by the following general formula (G1) or (G2) can be used.

In the general formulae (G1) and (G2), A represents a substituted or unsubstituted fused aromatic ring having 10 to 30 carbon atoms or a substituted or unsubstituted fused heteroaromatic ring having 10 to 30 carbon atoms, ^Ar1 to ^Ar6 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 13 carbon atoms, ^X1 to ^X12 each independently represent any one of a branched alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms. ^R1 to ^R10 each independently represent any one of hydrogen, an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 12 carbon atoms.

As the aromatic hydrocarbon group having 6 to 13 carbon atoms, phenyl, biphenyl, naphthyl, fluorenyl, etc. can be cited. Note that the aromatic hydrocarbon group is not limited thereto. In addition, when the aromatic hydrocarbon group has a substituent, as the substituent, alkyl groups having 1 to 7 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, dibutyl, tertiary butyl, pentyl, hexyl, etc., cycloalkyl groups having 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, cycloheptyl, 8,9,10-trinorbornyl, phenyl, naphthyl, biphenyl, etc., aryl groups having 6 to 12 carbon atoms, etc. can be cited.

In the general formula (G1), a substituted or unsubstituted fused aromatic ring having 10 to 30 carbon atoms or a substituted or unsubstituted fused heteroaromatic ring having 10 to 30 carbon atoms represents the above-mentioned luminescent body, and the above-mentioned skeleton can be used. In the general formulas (G1) and (G2), ^X1 to ^X12 represent a protecting group.

In the general formula (G2), the protecting group is bonded to the quinacridone skeleton, which is the luminescent body, via the aryl group. By adopting this structure, the protecting group can be arranged in a manner covering the luminescent body, so that the energy transfer based on the Dexter mechanism can be suppressed. In addition, the protecting group can also be directly bonded to the luminescent body.

As the energy acceptor material, an organic compound represented by the following general formula (G3) or (G4) can be used.

In the general formulae (G3) and (G4), A represents a substituted or unsubstituted fused aromatic ring having 10 to 30 carbon atoms or a substituted or unsubstituted fused heteroaromatic ring having 10 to 30 carbon atoms, and ^X1 to ^X12 each independently represent any one of a branched alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms.

The protecting group is preferably bonded to the luminescent body via a phenyl group. By adopting this structure, the protecting group can be arranged in a manner covering the luminescent body, so that energy transfer based on the Dexter mechanism can be suppressed. In addition, when the luminescent body and the protecting group are bonded via a phenyl group and two protecting groups are bonded to the phenyl group, as shown in general formulae (G3) and (G4), the two protecting groups are preferably bonded to the phenyl group at the meta position. By adopting this structure, the luminescent body can be efficiently covered, so that energy transfer based on the Dexter mechanism can be suppressed. As an example of an organic compound represented by general formula (G3), the above-mentioned 2tBu-mmtBuDPhA2Anth can be cited. That is, in one embodiment of the present invention, general formula (G3) is a particularly preferred example.

As the energy acceptor, an organic compound represented by the following general formula (G5) can be used.

In the general formula (G5), ^X1 to ^X8 each independently represent any one of a branched alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms, and ^R11 to ^R18 each independently represent any one of hydrogen, a branched alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, a trialkylsilyl group having 3 to 10 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 25 carbon atoms.

Examples of the aryl group having 6 to 25 carbon atoms include phenyl, naphthyl, biphenyl, fluorenyl, spirofluorenyl, etc. Note that the aryl group having 6 to 25 carbon atoms is not limited thereto. In addition, when the aryl group has a substituent, examples of the substituent include an alkyl group having 1 to 10 carbon atoms, a branched alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms.

Anthracene compounds have high light emission quantum yields and their light emitting bodies have small areas, so the upper and lower surfaces of anthracene can be efficiently covered with protective groups. An example of an organic compound represented by general formula (G5) is the above-mentioned 2tBu-mmtBuDPhA2Anth.

Examples of compounds listed in general formulae (G1) to (G5) are shown below by structural formulae (102) to (105) and (200) to (249). Note that the compounds listed in general formulae (G1) to (G5) are not limited thereto. In addition, the compounds represented by structural formulae (102) to (105) and (200) to (249) can be appropriately used as a guest material of a light-emitting element of an embodiment of the present invention. Note that the guest material is not limited thereto.

Structural formulas (100) and (101) show examples of materials that can be suitably used as a guest material of a light-emitting device according to an embodiment of the present invention. Note that the guest material is not limited thereto.

As compound 133, a phosphorescent material having a five-membered ring skeleton can be used. As the phosphorescent material, iridium, rhodium, platinum-based organic metal complexes or metal complexes can be cited. In addition, platinum complexes or organic iridium complexes having porphyrin ligands can be cited, and in particular, for example, organic iridium complexes such as iridium-based ortho-metal complexes are preferably used. As ortho-metallated ligands, pyrrole ligands, pyrazole ligands, 4H-triazole ligands, 1H-triazole ligands, imidazole ligands, benzimidazole ligands, naphthylimidazole ligands, etc. can be cited. At this time, compound 133 (phosphorescent material) has an absorption band with a triple MLCT (metal to ligand charge transfer) transition. In addition, it is preferred to select compound 133 and compound 132 (fluorescent material) in such a way that the luminescence peak of compound 133 overlaps with the absorption band on the longest wavelength side (low energy side) of compound 132 (fluorescent material). In this way, a light-emitting element with significantly improved luminescence efficiency can be achieved. In addition, even if compound 133 is a phosphorescent material, it can form an excited complex with compound 131. When an excited complex is formed, the phosphorescent material does not need to emit light at room temperature, and it only needs to be able to emit light at room temperature when the excited complex is formed. At this time, for example, tris[2-(1H-pyrazol-1-yl-κN2)phenyl-κC]iridium (III) (abbreviated as: Ir(ppz) ₃ ) and the like can be used as a phosphorescent material.

Examples of substances having a blue or green emission peak include tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviated as Ir(mpptz-dmp) ₃ ), tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazole)iridium(III) (abbreviated as Ir(Mptz) ₃ ), tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazole]iridium(III) (abbreviated as Ir(iPrptz-3b) ₃ ）、Tris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazole] iridium(III)(abbreviated as: Ir(iPr5btz) ₃ ）、Tris{2-[4-(4-cyano-2,6-diisobutylphenyl)-5-(2-methylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC} iridium(III)(abbreviated as: Ir(mpptz-diBuCNp) ₃ ）、Tris{2-[5-(2-methylphenyl)-4-(2,6-diisopropylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC} iridium(III)(abbreviated as: Ir(mpptz-diPrp) ₃ ) and other organometallic iridium complexes with a 4H-triazole skeleton; tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazole] iridium(III) (abbreviated as: Ir(Mptz1-mp) ₃ ), tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole) iridium(III) (abbreviated as: Ir(Prptz1-Me) ₃ ) and other organometallic iridium complexes with a 1H-triazole skeleton; fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole] iridium(III) (abbreviated as: Ir(iPrpmi) ₃ ), tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato] iridium(III) (abbreviated as Ir(dmpimpt-Me) ₃ ), tris{2-[1-(4-cyano-2,6-diisobutylphenyl)-1H-benzimidazol-2-yl-κN3]phenyl-κC}iridium(III) (abbreviated as Ir(pbi-diBuCNp) ₃ ), (OC-6-22)-tris{2-[1-(2,6-diisobutylphenyl)-1H-benzimidazol-2-yl-κN3]phenyl-κC}iridium(III) (abbreviated as Ir(pbi-diBuCNp) ₃ ) and other organometallic iridium complexes having a benzimidazole skeleton; bis{2-[1-(2,6-diisobutylphenyl)-1H-naphtho[1,2-d]imidazol-2-yl-κN3]phenyl-κC}[2-(4-toluene-5-phenyl-2-pyridyl-κN2)phenyl-κC]iridium(III) (abbreviated as Ir(pni-diBup) ₂ (mdppy)), tris{2-[1-(2,6-diisobutylphenyl)-1H-naphtho[1,2-d]imidazol-2-yl-κN3]phenyl-κC}iridium(III) (abbreviated as Ir(pni-diBup) ₃ ) and other organometallic iridium complexes having a naphthoimidazole skeleton. Among the above materials, organic metal iridium complexes having a nitrogen-containing five-membered heterocyclic skeleton such as a 4H-triazole skeleton, a 1H-triazole skeleton, an imidazole skeleton, a benzimidazole skeleton, and a naphthylimidazole skeleton are particularly preferred because of their high triplet excitation energy, high reliability, and high luminescence efficiency. In addition, platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum (II) (abbreviated as: PtOEP) and rare earth metal complexes such as tris[1-(2-thienylcarbonyl)-3,3,3-trifluoroacetone](monomorphin)piperidinium (III) (abbreviated as: Eu(TTA) ₃ (Phen)) can also be used.

In addition, for example, a TADF material can be used as the compound 134. Preferably, the energy difference between the S1 energy level and the T1 energy level of the compound 134 is small, specifically, greater than 0 eV and less than 0.2 eV.

Compound 134 preferably includes a skeleton having hole transport properties and a skeleton having electron transport properties. Alternatively, compound 134 preferably includes a π-electron-rich skeleton or an aromatic amine skeleton and a π-electron-deficient skeleton. This makes it easy to form a donor-acceptor type excited state in the molecule. Furthermore, preferably, a structure in which a skeleton having electron transport properties is directly bonded to a skeleton having hole transport properties in a manner that simultaneously enhances the donor property and the acceptor property in the molecule of compound 134. Alternatively, preferably, a structure in which a π-electron-rich skeleton or an aromatic amine skeleton is directly bonded to a π-electron-deficient skeleton. By enhancing both the donor property and the acceptor property in the molecule, the overlapped region of the HOMO and LUMO molecular orbital distributions in compound 134 can be reduced, thereby reducing the energy difference between the singlet excitation energy level and the triplet excitation energy level of compound 134. In addition, the triplet excitation energy level of compound 134 can be kept high.

When the TADF material is composed of one material, for example, the following materials can be used.

First, fullerene or its derivatives, acridine derivatives such as proflavin, eosin, etc. Also, metal-containing porphyrins containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd) can be cited. Examples of the metal-containing porphyrin include protoporphyrin-tin fluoride complex (SnF ₂ (Proto IX)), mesoporphyrin-tin fluoride complex (SnF ₂ (Meso IX)), hematoporphyrin-tin fluoride complex (SnF ₂ (Hemato IX)), tetramethylnaphthoporphyrin-tin fluoride complex (SnF ₂ (Copro III-4Me)), octaethylporphyrin-tin fluoride complex (SnF ₂ (OEP)), protoporphyrin-tin fluoride complex (SnF ₂ (Etio I)), and octaethylporphyrin-platinum chloride complex (PtCl ₂ OEP).

In addition, as a heat-activated delayed fluorescence material composed of one material, a heterocyclic compound having a π-electron-rich skeleton and a π-electron-deficient skeleton can also be used. Specifically, 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazole-11-yl)-1,3,5-triazine (abbreviated as: PIC-TRZ), 2-{4-[3-(N-phenyl-9H-carbazole-3-yl)-9H-carbazole-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviated as: PCCzPTzn), 2-[4-(10 H-phenanthracene-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviated as PXZ-TRZ), 3-[4-(5-phenyl-5,10-dihydrophenanthracene-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviated as PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-oxanthracen-9-one (abbreviated as ACRXTN), Bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (abbreviated as: DMAC-DPS), 10-phenyl-10H,10'H-spiro[acridine-9,9'-anthracen]-10'-one (abbreviated as: ACRSA), 4-(9'-phenyl-3,3'-bi-9H-carbazole-9-yl)benzofurano[3,2-d]pyrimidine (abbreviated as: 4PCCzBfpm), 4-[4-(9'- A heterocyclic compound having one or both of a π-electron-rich skeleton and a π-electron-deficient skeleton, such as phenyl-3,3'-bi-9H-carbazole-9-yl)phenyl]benzofurano[3,2-d]pyrimidine (abbreviated as 4PCCzPBfpm), 9-[3-(4,6-diphenyl-1,3,5-triazine-2-yl)phenyl]-9'-phenyl-2,3'-bi-9H-carbazole (abbreviated as mPCCzPTzn-02). The heterocyclic compound has a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring, and thus has high electron and hole transport properties, and is therefore preferred. In particular, among the skeletons having π-electron-deficient heteroaromatic rings, pyridine skeletons, diazine skeletons (pyrimidine skeletons, pyrazine skeletons, pyrimidine skeletons) and triazine skeletons are stable and have good reliability, so they are preferred. In particular, the benzofuranopyrimidine skeleton, benzothiophenopyrimidine skeleton, benzofuranopyrazine skeleton, and benzothiophenopyrazine skeleton have high acceptor properties and good reliability, so they are preferred. In addition, among the skeletons having π-electron-rich heteroaromatic rings, acridine skeletons, phenanthrene skeletons, phenanthrenethiophene skeletons, furan skeletons, thiophene skeletons, and pyrrole skeletons are stable and have good reliability, so it is preferred to have at least one of the above skeletons. In addition, it is preferred to use a dibenzofuran skeleton as a furan skeleton, and it is preferred to use a dibenzothiophene skeleton as a thiophene skeleton. As the pyrrole skeleton, it is particularly preferred to use an indole skeleton, a carbazole skeleton, a bicarbazole skeleton, and a 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton. In addition, in a substance in which a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring are directly bonded, the donor property of the π-electron-rich heteroaromatic ring and the acceptor property of the π-electron-deficient heteroaromatic ring are both strong, and the difference in energy levels between the singlet excited state and the triplet excited state becomes smaller, so it is particularly preferred. In addition, an aromatic ring bonded to an electron-withdrawing group such as a cyano group can also be used instead of a π-electron-deficient heteroaromatic ring. In addition, as a π-electron-rich skeleton, an aromatic amine skeleton, a phenazine skeleton, etc. can be used. In addition, as the π-electron-deficient skeleton, an anthracene skeleton, a thioxanthene dioxide skeleton, a triazole skeleton, an imidazole skeleton, an anthraquinone skeleton, a boron-containing skeleton such as phenylborane or boranthrene, an aromatic ring or a heteroaromatic ring having a nitrile group or a cyano group such as benzonitrile or cyanophenyl, a carbonyl skeleton such as benzophenone, a phosphine oxide skeleton, a sulfonium skeleton, etc. can be used. In this way, a π-electron-deficient skeleton and a π-electron-rich skeleton can be used to replace at least one of the π-electron-deficient heteroaromatic ring and the π-electron-rich heteroaromatic ring.

When compound 134 does not have the function of converting triplet excitons into luminescence, the combination of compound 131 and compound 133 or the combination of compound 131 and compound 134 is preferably a combination that forms an excited state complex with each other, but there is no particular limitation. Preferably, one has the function of transporting electrons and the other has the function of transporting holes.

As compound 131, in addition to zinc and aluminum metal complexes, there can be cited diazole derivatives, triazole derivatives, benzimidazole derivatives, quinoline derivatives, dibenzoquinoline derivatives, dibenzothiophene derivatives, dibenzofuran derivatives, pyrimidine derivatives, triazine derivatives, pyridine derivatives, bipyridine derivatives, phenanthroline derivatives, etc. As other examples, there can be cited aromatic amines and carbazole derivatives.

In addition, for example, the following hole-transporting materials and electron-transporting materials can be used.

As the hole transport material, a material having higher hole transport than electron transport can be used, preferably a material having a hole mobility of 1×10 ^-6 cm ² /Vs or more. Specifically, aromatic amines, carbazole derivatives, aromatic hydrocarbons, stilbene derivatives, etc. can be used. The hole transport material may also be a polymer compound.

As materials with high hole transport properties, for example, aromatic amine compounds include N,N'-di(p-tolyl)-N,N'-diphenyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4'-bis[N-(4-diphenylaminophenyl)-N-anilino]biphenyl (abbreviation: DPAB), N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (abbreviation: DNTPD), and 1,3,5-tris[N-(4-diphenylaminophenyl)-N-anilino]benzene (abbreviation: DPA3B).

In addition, as carbazole derivatives, specifically, 3-[N-(4-diphenylaminophenyl)-N-anilino]-9-phenylcarbazole (abbreviated as PCzDPA1), 3,6-bis[N-(4-diphenylaminophenyl)-N-anilino]-9-phenylcarbazole (abbreviated as PCzDPA2), 3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviated as PCzDPA2) and 3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviated as PCzDPA3) can be cited. : PCzTPN2), 3-[N-(9-phenylcarbazole-3-yl)-N-anilino]-9-phenylcarbazole (abbreviated as: PCzPCA1), 3,6-bis[N-(9-phenylcarbazole-3-yl)-N-anilino]-9-phenylcarbazole (abbreviated as: PCzPCA2), 3-[N-(1-naphthyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole (abbreviated as: PCzPCN1), etc.

In addition, examples of carbazole derivatives include 4,4'-di(N-carbazolyl)biphenyl (abbreviated as CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviated as TCPB), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviated as CzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

Examples of the aromatic hydrocarbon include 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene (abbreviation: t-BuAnth), and 9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA). , 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9'-bianthracene, 10,10'-diphenyl-9,9'-bianthracene, 10,10'-bis(2-phenylphenyl)-9,9'-bianthracene, 10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthracene, anthracene, fused tetraphenyl, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, etc. In addition, fused pentadiene, coronene, etc. can also be used. Thus, it is more preferable to use an aromatic hydrocarbon having a hole mobility of 1×10 ^-6 cm ² /Vs or more and having 14 to 42 carbon atoms.

Note that the aromatic hydrocarbon may have a vinyl skeleton. Examples of aromatic hydrocarbons having a vinyl group include 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA).

In addition, high molecular weight compounds such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N’-[4-(4-diphenylamino)phenyl]phenyl-N’-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), and poly[N,N’-bis(4-butylphenyl)-N,N’-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can also be used.

In addition, as a material with high hole transport properties, for example, 4,4'-bis[N-(1-naphthyl)-N-anilino]biphenyl (abbreviated as: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviated as: TPD), 4,4',4''-tris(carbazol-9-yl)triphenylamine (abbreviated as: TCTA), 4,4',4''-tris[N-(1-naphthyl)- N-anilino]triphenylamine (abbreviated as: 1'-TNATA), 4,4',4''-tris(N,N-diphenylamino)triphenylamine (abbreviated as: TDATA), 4,4',4''-tris[N-(3-methylphenyl)-N-anilino]triphenylamine (abbreviated as: MTDATA), 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-anilino]biphenyl (abbreviated as: BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)- )triphenylamine (abbreviated as BPAFLP), 4-phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine (abbreviated as mBPAFLP), N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{(9,9-dimethyl-2-[N'-phenyl-N'-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviated as DFLADFL), N-(9,9-dimethyl-2-diphenylamino-9 H-fluoren-7-yl) diphenylamine (abbreviated as: DPNF), 2-[N-(4-diphenylaminophenyl)-N-anilino]spiro-9,9'-bifluoren-7-yl) (abbreviated as: DPASF), 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviated as: PCBA1BP), 4,4'-diphenyl-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviated as: PCBBi1BP), 4-(1-naphthyl)-4' -(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviated as: PCBANB), 4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviated as: PCBNBB), 4-phenyldiphenyl-(9-phenyl-9H-carbazole-3-yl)amine (abbreviated as: PCA1BP), N,N'-bis(9-phenylcarbazole-3-yl)-N,N'-diphenylbenzene-1,3-diamine (abbreviated as: PCA2B) 、N,N',N''-triphenyl-N,N',N''-tri(9-phenylcarbazole-3-yl)benzene-1,3,5-triamine (abbreviated as: PCA3B), N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazole-3-amine (abbreviated as: PCBiF), N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9,9-dimethyl-9 H-fluorene-2-amine (abbreviated as: PCBBiF), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]fluorene-2-amine (abbreviated as: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]spiro-9,9'-bifluorene-2-amine (abbreviated as: PCBASF), 2-[N-(9-phenylcarbazole-3-yl)-N-anilino]spiro-9,9'-bifluorene (abbreviated as: : PCASF), 2,7-bis[N-(4-diphenylaminophenyl)-N-anilino]spiro-9,9'-bifluorene (abbreviated as: DPA2SF), N-[4-(9H-carbazol-9-yl)phenyl]-N-(4-phenyl)phenylaniline (abbreviated as: YGA1BP), N,N'-bis[4-(carbazol-9-yl)phenyl]-N,N'-diphenyl-9,9-dimethylfluorene-2,7-diamine (abbreviated as: YGA2F) and other aromatic amine compounds. In addition, 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviated as PCPN), 3-[4-(9-phenanthrenyl)-phenyl]-9-phenyl-9H-carbazole (abbreviated as PCPPn), 3,3'-bis(9-phenyl-9H-carbazole) (abbreviated as PCCP), 1,3-bis(N-carbazolyl)benzene (abbreviated as mCP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviated as CzTP), 4-{(3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviated as mmDBFFLBi-II), 4,4',4''-(benzene-1,3,5-triyl)tris(dibenzofuran) (abbreviated as mCP) can be used. amine compounds, carbazole compounds, thiophene compounds, furan compounds, fluorene compounds, triphenyl compounds, phenanthrene compounds, etc., such as 1,3,5-tris(dibenzothiophene-4-yl)benzene (abbreviated as DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviated as DBTFLP-III), 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviated as DBTFLP-IV), 4-[3-(triphenyl-2-yl)phenyl]dibenzothiophene (abbreviated as mDBTPTp-II). The substances described here are mainly 1×10 ^-6 cm ² /Vs or more. However, any substance other than the above substances may be used as long as it has a hole-transmitting property higher than an electron-transmitting property.

As the electron-transmitting material, a material having higher electron-transmitting property than hole-transmitting property can be used, and preferably a material having an electron mobility of 1×10 ^-6 cm ² /Vs or more can be used. As the material that easily receives electrons (material having electron-transmitting property), π-electron-deficient heteroaromatic compounds such as nitrogen-containing heteroaromatic compounds or metal complexes can be used. As specific examples, metal complexes including quinoline ligands, benzoquinoline ligands, oxadiazole ligands or thiazole ligands, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, pyridine derivatives, bipyridine derivatives, pyrimidine derivatives, and the like can be cited.

For example, a metal complex having a quinoline skeleton or a benzoquinoline skeleton such as tris(8-hydroxyquinolinato)aluminum(III) (abbreviation: Alq), tris(4-methyl-8-hydroxyquinolinato)aluminum(III) (abbreviation: Almq ₃ ), bis(10-hydroxybenzo[h]quinolinato)borate(II) (abbreviation: BeBq ₂ ), bis(2-methyl-8-hydroxyquinolinato)(4-phenylphenol)aluminum(III) (abbreviation: BAlq), bis(8-hydroxyquinolinato)zinc(II) (abbreviation: Znq) and the like can be used. In addition to these, metal complexes having oxazolyl or thiazole ligands such as bis[2-(2-benzoxazolyl)phenol]zinc(II) (abbreviated as ZnPBO) and bis[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated as ZnBTZ) can also be used. In addition to the metal complex, 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazole-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 2,2',2''-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), 2-[3-(dibenzothiophene-4 -yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviated as: mDBTBIm-II), red phenanthroline (abbreviated as: BPhen), 2,9-bis(naphthalene-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviated as: NBPhen), bathocophine (abbreviated as: BCP) and other heterocyclic compounds; 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline (abbreviated as: 2mDBTPDBq-II), 2-[3'-(dibenzothiophene-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoline (abbreviated as: 2mDBTBPDBq-II), 2-[3'-(9H-carbazole-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoline (abbreviated as: 2m CzBPDBq), 2-[4-(3,6-diphenyl-9H-carbazole-9-yl)phenyl]dibenzo[f,h]quinoline (abbreviated as: 2CzPDBq-III), 7-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline (abbreviated as: 7mDBTPDBq-II), 6-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline (abbreviated as: 6mDBTPDBq-II), 4,6-bis[3-(phenanthrene-9-yl)phenyl]pyrimidine (abbreviated as: 4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothiophene-1-yl)phenyl]pyrimidine (abbreviated as: 4,6mDBTP2Pm-II), 4,6-bis[3-(9H -carbazole-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm) and other heterocyclic compounds with a diazine skeleton; 2-{4-[3-(N-phenyl-9H-carbazole-3-yl)-9H-carbazole-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn) and other heterocyclic compounds with a triazine skeleton; 3,5-bis[3-(9H-carbazole-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), 1,3,5-tris[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB) and other heterocyclic compounds with a pyridine skeleton; 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) and other heteroaromatic compounds. In addition, polymer compounds such as poly(2,5-pyridinediyl) (abbreviation: PPy), poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py), and poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2'-bipyridine-6,6'-diyl)] (abbreviation: PF-BPy) can also be used. The substances described here are mainly substances having an electron mobility of 1×10 ^-6 cm ² /Vs or more. Note that substances other than the above substances can be used as long as they have higher electron transport properties than hole transport properties.

Compound 134 is preferably a material that can form an excited state complex with compound 131. Specifically, the hole transporting material and the electron transporting material shown above can be used. At this time, compound 131 and compound 134 are selected in such a way that the luminescence peak of the excited state complex formed by compound 131 and compound 134 overlaps with the absorption band of compound 133 (phosphorescent material having a five-membered ring skeleton) on the longest wavelength side (low energy side). Thus, a light-emitting element with significantly improved luminescence efficiency can be achieved.

The light-emitting layer 130 may also be formed of two or more layers. For example, when the light-emitting layer 130 is formed by stacking a first light-emitting layer and a second light-emitting layer in sequence from one side of the hole transport layer, a substance having hole transport properties may be used as a main material of the first light-emitting layer, and a substance having electron transport properties may be used as a main material of the second light-emitting layer.

Furthermore, the light-emitting layer 130 may contain a material (compound 135) other than compound 131, compound 132, compound 133, and compound 134. In this case, in order to allow compound 131 and compound 133 (or compound 134) to efficiently form an excited complex, it is preferred that the HOMO energy level of one of compound 131 and compound 133 (or compound 134) is the highest among the materials in the light-emitting layer 130, and the LUMO energy level of the other of compound 131 and compound 132 is the lowest among the materials in the light-emitting layer 130. By adopting such an energy level correlation, the reaction of compound 131 and compound 135 to form an excited complex can be suppressed.

For example, when compound 131 has hole transport properties and compound 133 (or compound 134) has electron transport properties, it is preferred that the HOMO energy level of compound 131 is higher than the HOMO energy level of compound 133 and the HOMO energy level of compound 135, and the LUMO energy level of compound 133 is lower than the LUMO energy level of compound 131 and the LUMO energy level of compound 135. In this case, the LUMO energy level of compound 135 may be higher or lower than the LUMO energy level of compound 131. In addition, the HOMO energy level of compound 135 may be higher or lower than the HOMO energy level of compound 133.

Although there is no particular limitation on the material (compound 135) that can be used for the light-emitting layer 130, for example, tris(8-hydroxyquinoline)aluminum(III) (abbreviated as Alq), tris(4-methyl-8-hydroxyquinoline)aluminum(III) (abbreviated as Almq ₃ ), bis(10-hydroxybenzo[h]quinoline)borate(II) (abbreviated as BeBq ₂ ), bis(2-methyl-8-hydroxyquinoline)(4-phenylphenol)aluminum(III) (abbreviated as BAlq), bis(8-hydroxyquinoline)zinc(II) (abbreviated as Znq), bis[2-(2-benzoxazolyl)phenol]zinc(II) (abbreviated as ZnPBO), bis[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated as ZnBTZ) and other metal complexes Compounds; 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (OXD-7), 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ) 、2,2',2''-(1,3,5-phenyltriyl)tris(1-phenyl-1H-benzimidazole)(abbreviated as: TPBI), red phenanthroline (abbreviated as: BPhen), bathocophine (abbreviated as: BCP), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviated as: CO11) and other heterocyclic compounds; 4,4'-bis[N- Aromatic amine compounds include (1-naphthyl)-N-phenylamino]biphenyl (abbreviated as NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviated as TPD), and 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviated as BSPB). In addition, condensed polycyclic aromatic compounds such as anthracene derivatives, phenanthrene derivatives, pyrene derivatives, chrysene derivatives, and dibenzo[g,p]chrysene derivatives can be mentioned. Specifically, 9,10-diphenylanthracene (DPAnth), N,N-diphenyl-9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole-3-amine (CzA1PA), 4-(10-phenyl-9-anthracenyl)triphenylamine (DPhPA), 4-(9H-carbazole-9-yl)-4'-(10-phenyl-9-anthracenyl)triphenylamine (YGAPA), N,9-diphenyl-N-[4- (10-phenyl-9-anthracenyl)phenyl]-9H-carbazole-3-amine (abbreviated as: PCAPA), N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthracenyl)phenyl]phenyl}-9H-carbazole-3-amine (abbreviated as: PCAPBA), N,9-diphenyl-N-(9,10-diphenyl-2-anthracenyl)-9H-carbazole-3-amine (abbreviated as: 2PCAPA), 6,12-dimethoxy-5,11-diphenylchrysene, N,N,N',N',N'',N'',N''',N'''-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetramine (abbreviated as: DBC1), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviated as: CzPA), 3,6-diphenyl-9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviated as: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviated as: DPP A), 9,10-di(2-naphthyl)anthracene (DNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA), 9,9'-bianthracene (BANT), 9,9'-(stilbene-3,3'-diyl)phenanthrene (DPNS), 9,9'-(stilbene-4,4'-diyl)phenanthrene (DPNS2), and 1,3,5-tri(1-pyrene)benzene (TPB3). From these substances and known substances, one or more substances having a larger energy gap than the energy gap of the above-mentioned compounds 131 and 132 can be selected.

<<A pair of electrodes>> Electrode 101 and electrode 102 have the function of injecting holes and electrons into the light-emitting layer 130. Electrode 101 and electrode 102 can be formed using metals, alloys, conductive compounds, and mixtures or stacks thereof. A typical example of metal is aluminum (Al), and in addition, transition metals such as silver (Ag), tungsten, chromium, molybdenum, copper, and titanium; alkali metals such as lithium (Li) or cesium; and Group 2 metals such as calcium or magnesium (Mg) can be used. As a transition metal, a rare earth metal such as ytterbium (Yb) can also be used. As an alloy, an alloy including the above metals can be used, for example, MgAg, AlLi, etc. As the conductive compound, for example, metal oxides such as indium tin oxide (hereinafter referred to as ITO), indium tin oxide containing silicon or silicon oxide (abbreviated as: ITSO), indium zinc oxide (Indium Zinc Oxide), and indium oxide containing tungsten and zinc can be cited. Inorganic carbon materials such as graphene can also be used as the conductive compound. As described above, one or both of the electrode 101 and the electrode 102 can be formed by stacking a plurality of these materials.

In addition, the light obtained from the light-emitting layer 130 is extracted through one or both of the electrode 101 and the electrode 102. Therefore, at least one of the electrode 101 and the electrode 102 has the function of transmitting visible light. As a conductive material having a light-transmitting function, a conductive material having a visible light transmittance of 40% or more and 100% or less, preferably 60% or more and 100% or less, and a resistivity of 1× ^10-2 Ω∙cm or less can be cited. In addition, the electrode on the light-extracting side can also be formed of a conductive material having a light-transmitting function and a light-reflecting function. As the conductive material, a conductive material having a visible light reflectance of 20% or more and 80% or less, preferably 40% or more and 70% or less, and a resistivity of 1× ^10-2 Ω∙cm or less can be cited. When a material with low light transmittance such as metal or alloy is used for the light extracting electrode, one or both of the electrode 101 and the electrode 102 may be formed with a thickness that allows visible light to pass therethrough (for example, a thickness of 1 nm to 10 nm).

Note that in this specification, etc., as an electrode having a light-transmitting function, a material having a function of transmitting visible light and having conductivity may be used, such as an oxide conductive layer represented by ITO, an oxide semiconductor layer, or an organic conductive layer containing organic substances. As an organic conductive layer containing organic substances, for example, a layer containing a composite material formed by mixing an organic compound and an electron donor (donor), a layer containing a composite material formed by mixing an organic compound and an electron acceptor (acceptor), etc. can be cited. In addition, the resistivity of the transparent conductive layer is preferably 1×10 ⁵ Ω∙cm or less, and more preferably 1×10 ⁴ Ω∙cm or less.

In addition, as a film forming method of the electrode 101 and the electrode 102, a sputtering method, an evaporation method, a printing method, a coating method, an MBE (Molecular Beam Epitaxy) method, a CVD method, a pulsed laser deposition method, an ALD (Atomic Layer Deposition) method, or the like can be applied.

<<Hole injection layer>> The hole injection layer 111 has the function of reducing the injection barrier of holes from one of a pair of electrodes (electrode 101 or electrode 102) to promote hole injection, and is formed using, for example, transition metal oxides, phthalocyanine derivatives, or aromatic amines. Examples of transition metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganese oxide. Examples of phthalocyanine derivatives include phthalocyanine or metal phthalocyanine. Examples of aromatic amines include benzidine derivatives or phenylenediamine derivatives. Polymer compounds such as polythiophene or polyaniline may also be used, typically: poly(ethylenedioxythiophene)/poly(styrenesulfonic acid) as self-doped polythiophene.

As the hole injection layer 111, a layer of a composite material composed of a hole transport material and a material having the property of receiving electrons from the hole transport material can be used. Alternatively, a stack of a layer containing a material having the property of receiving electrons and a layer containing a hole transport material can be used. In a steady state or in the presence of an electric field, charge transfer can be performed between these materials. As materials having the property of receiving electrons, organic acceptors such as quinone dimethane derivatives, tetrachlorobenzoquinone derivatives, and hexaazatriphenylbenzene derivatives can be cited. Specifically, compounds having an electron-withdrawing group (especially a halogen group such as a fluorine group, or a cyano group) such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviated as F ₄ -TCNQ), chloranil, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviated as HAT-CN), and 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (abbreviated as F6-TCNNQ) can be cited. In particular, compounds such as HAT-CN in which an electron-withdrawing group is bonded to a condensed aromatic ring having a plurality of heteroatoms are thermally stable and therefore are preferred. In addition, [3] ylidene derivatives containing electron-withdrawing groups (especially halogen groups such as fluorine groups and cyano groups) are particularly preferred because of their very high electron accepting properties. Specifically, α, α', α''-1,2,3-cycloalkanetriylidene tris[4-cyano-2,3,5,6-tetrafluorophenylacetonitrile], α, α', α''-1,2,3-cyclopropanetriylidene tris[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)phenylacetonitrile], α, α', α''-1,2,3-cycloalkanetriylidene tris[2,3,4,5,6-pentafluorophenylacetonitrile], etc. can be cited. In addition, transition metal oxides, such as oxides of Group 4 to Group 8 metals, can be used. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, uranium oxide, etc. can be used. In particular, molybdenum oxide is preferably used because it is stable even in the atmosphere, has low hygroscopicity, and is easy to handle.

As the hole transport material, a material having a hole transport property higher than an electron transport property can be used, and preferably a material having a hole mobility of 1×10 ^-6 cm ² /Vs or more can be used. Specifically, aromatic amines and carbazole derivatives listed as hole transport materials that can be used for the light emitting layer 130 can be used. In addition, aromatic hydrocarbons and stilbene derivatives can also be used. The above-mentioned hole transport material can also be a polymer compound.

Examples of the aromatic hydrocarbon include 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene (abbreviation: t-BuAnth), and 9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA). , 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9'-bianthracene, 10,10'-diphenyl-9,9'-bianthracene, 10,10'-bis(2-phenylphenyl)-9,9'-bianthracene, 10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthracene, anthracene, fused tetraphenyl, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, etc. In addition, fused pentadiene, coronene, etc. can also be used. Thus, it is more preferable to use an aromatic hydrocarbon having a hole mobility of 1×10 ^-6 cm ² /Vs or more and having 14 to 42 carbon atoms.

Note that the aromatic hydrocarbon may have a vinyl skeleton. Examples of aromatic hydrocarbons having a vinyl group include 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA).

In addition, high molecular weight compounds such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N’-[4-(4-diphenylamino)phenyl]phenyl-N’-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), and poly[N,N’-bis(4-butylphenyl)-N,N’-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can also be used.

<<Hole transport layer>> The hole transport layer 112 is a layer containing a hole transport material, and the material exemplified as the material of the hole injection layer 111 can be used. The hole transport layer 112 has the function of transferring holes injected into the hole injection layer 111 to the light emitting layer 130, so it is preferred to have a HOMO energy level that is the same as or close to the HOMO energy level of the hole injection layer 111.

As the hole-transporting material, the materials exemplified as the materials of the hole injection layer 111 can be used. In addition, it is preferable to use a substance having a hole mobility of 1×10 ^-6 cm ² /Vs or more. However, as long as the hole-transporting property is higher than the electron-transporting property, a substance other than the above-mentioned substances can be used. In addition, the layer including the substance having high hole-transporting property is not limited to a single layer, and two or more layers composed of the above-mentioned substances can be stacked.

＜＜Electron transport layer＞＞ The electron transport layer 118 has a function of transporting electrons injected from the other of a pair of electrodes (electrode 101 or electrode 102) through the electron injection layer 119 to the light-emitting layer 130. As the electron transport material, a material having higher electron transport than hole transport can be used, and preferably a material having an electron mobility of 1× ^{10-6 cm2} /Vs or more can be used. As a compound that easily receives electrons (a material having electron transport), a π-electron-deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound or a metal complex can be used. Specifically, metal complexes including quinoline ligands, benzoquinoline ligands, oxazole ligands, or thiazole ligands can be cited as electron transport materials that can be used for the light-emitting layer 130. In addition, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, pyridine derivatives, bipyridine derivatives, pyrimidine derivatives, etc. can be cited. In addition, a substance having an electron mobility of 1×10 ^-6 cm ² /Vs or more is preferred. However, as the electron transport layer, as long as the electron transport property is higher than the hole transport property, a substance other than the above can be used. In addition, the electron transport layer 118 is not limited to a single layer, and two or more layers composed of the above substances can be stacked.

In addition, a layer for controlling the movement of electron carriers can be provided between the electron transport layer 118 and the light emitting layer 130. The layer for controlling the movement of electron carriers is a layer in which a small amount of a substance with high electron capture property is added to the above-mentioned material with high electron transport property, and the balance of carriers can be adjusted by suppressing the movement of electron carriers. This structure has a great effect on suppressing problems caused by electrons passing through the light emitting layer (such as a reduction in the life of the device).

＜＜Electron injection layer＞＞ The electron injection layer 119 has the function of lowering the injection barrier of electrons from the electrode 102 to promote electron injection, and for example, Group 1 metals, Group 2 metals or their oxides, halides, carbonates, etc. can be used. A composite material of the above-mentioned electron-transmitting material and a material having the property of supplying electrons to the electron-transmitting material can also be used. As the material having the electron-supplying property, Group 1 metals, Group 2 metals or their oxides, etc. can be cited. Specifically, alkaline metals, alkaline earth metals or compounds of these metals such as lithium fluoride (LiF), sodium fluoride (NaF), cesium fluoride (CsF), calcium fluoride (CaF ₂ ) and lithium oxide (LiO _x ) can be used. In addition, rare earth metal compounds such as erbium fluoride (ErF ₃ ) can be used. Alternatively, an electron salt may be used for the electron injection layer 119. Examples of the electron salt include a mixed oxide of calcium and aluminum to which electrons are added at a high concentration. Alternatively, a substance that can be used for the electron transport layer 118 may be used for the electron injection layer 119.

In addition, a composite material formed by mixing an organic compound with an electron donor can also be used for the electron injection layer 119. This composite material has excellent electron injection and electron transport properties because the electron donor generates electrons in the organic compound. In this case, the organic compound is preferably a material that has excellent performance in transporting the generated electrons. Specifically, for example, the substances constituting the electron transport layer 118 as described above (metal complexes, heteroaromatic compounds, etc.) can be used. As an electron donor, any substance that can donate electrons to the organic compound can be used. Specifically, it is preferred to use alkali metals, alkali earth metals, and rare earth metals, and lithium, cesium, magnesium, calcium, beryl, and yttrium can be mentioned. In addition, it is preferred to use an alkali metal oxide or an alkali earth metal oxide, and lithium oxide, calcium oxide, barium oxide, etc. can be mentioned. In addition, a Lewis base such as magnesium oxide can also be used. In addition, an organic compound such as tetrathiafulvalene (abbreviated as: TTF) can also be used.

In addition, the above-mentioned light-emitting layer, hole injection layer, hole transport layer, electron transport layer and electron injection layer can be formed by evaporation (including vacuum evaporation), inkjet method, coating method, nozzle printing method, gravure printing, etc. In addition, as the above-mentioned light-emitting layer, hole injection layer, hole transport layer, electron transport layer and electron injection layer, in addition to the above-mentioned materials, inorganic compounds such as quantum dots or high molecular compounds (oligomers, dendrimers, polymers, etc.) can also be used.

As quantum dots, colloidal quantum dots, alloy quantum dots, core-shell quantum dots, core-type quantum dots, etc. can be used. In addition, quantum dots containing element groups of Group 2 and Group 16, Group 13 and Group 15, Group 13 and Group 17, Group 11 and Group 17, or Group 14 and Group 15 can also be used. Alternatively, quantum dots containing elements such as cadmium (Cd), selenium (Se), zinc (Zn), sulfur (S), phosphorus (P), indium (In), tellurium (Te), lead (Pb), gallium (Ga), arsenic (As), aluminum (Al) can be used.

As the liquid medium used for wet treatment, for example, ketones such as methyl ethyl ketone and cyclohexanone; glycerol fatty acid esters such as ethyl acetate; halogenated aromatic hydrocarbons such as dichlorobenzene; aromatic hydrocarbons such as toluene, xylene, mesitylene, cyclohexylbenzene; aliphatic hydrocarbons such as cyclohexane, decahydronaphthalene, dodecane; and organic solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).

Examples of polymer compounds that can be used in the light-emitting layer include polyphenylene vinylene (PPV) derivatives such as poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (abbreviated as MEH-PPV) and poly(2,5-dioctyl-1,4-phenylene vinylene); polyfluorene derivatives such as poly(9,9-di-n-octylfluorenyl-2,7-diyl) (abbreviated as PF8), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)] (abbreviated as F8BT), poly[( [(9,9-dioctylfluorenyl-2,7-diyl)-alt-(2,2'-bithiophene-5,5'-diyl)] (abbreviated as F8T2), poly[(9,9-dioctyl-2,7-divinylfluorenyl)-alt-(9,10-anthracene)], poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-(2,5-dimethyl-1,4-phenylene)], etc.; polyalkylthiophene (PAT) derivatives such as poly(3-hexylthiophene-2,5-diyl) (abbreviated as P3HT), etc., polyphenylene derivatives, etc. In addition, the above-mentioned polymer compounds, poly(N-vinylcarbazole) (abbreviated as PVK), poly(2-vinylnaphthalene), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (abbreviated as PTAA) and other polymer compounds may be doped with luminescent compounds and used in the luminescent layer. As the luminescent compound, the luminescent compounds exemplified above may be used.

<<Substrate>> In addition, the light-emitting element of one embodiment of the present invention can be manufactured on a substrate made of glass, plastic, etc. As the order of stacking on the substrate, it can be stacked in sequence from the electrode 101 side or from the electrode 102 side.

In addition, as a substrate for a light-emitting element that can form an embodiment of the present invention, for example, glass, quartz or plastic can be used. Alternatively, a flexible substrate can also be used. A flexible substrate is a substrate that can be bent, such as a plastic substrate made of polycarbonate or polyarylate. In addition, a film, an inorganic evaporated film, etc. can be used. Note that other materials can be used as long as they serve as a support in the manufacturing process of the light-emitting element and the optical device. Alternatively, any material can be used as long as it has the function of protecting the light-emitting element and the optical device.

For example, in this specification, etc., various substrates can be used to form a light-emitting element. There is no particular limitation on the type of substrate. As examples of the substrate, for example, a semiconductor substrate (for example, a single crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate with a stainless steel foil, a tungsten substrate, a substrate with a tungsten foil, a flexible substrate, a bonding film, a cellulose nanofiber (CNF) containing a fibrous material, paper or a base film, etc. can be used. As examples of glass substrates, there are barium borosilicate glass, aluminum borosilicate glass, sodium calcium glass, etc. As flexible substrates, bonding films, base films, etc., the following examples can be cited. For example, plastics represented by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), and polytetrafluoroethylene (PTFE) can be cited. Alternatively, resins such as acrylic resins can be cited as an example. Alternatively, polypropylene, polyester, polyvinyl fluoride, or polyvinyl chloride can be cited as an example. Alternatively, polyamide, polyimide, aromatic polyamide, epoxy resin, inorganic vapor-deposited film, paper, etc. can be cited as an example.

In addition, a flexible substrate may be used as a substrate, and a light-emitting element may be directly formed on the flexible substrate. Alternatively, a peeling layer may be provided between the substrate and the light-emitting element. The peeling layer may be used when a part or all of the light-emitting element is manufactured on the peeling layer, and then it is separated from the substrate and transferred to another substrate. In this case, the light-emitting element may be transferred to a substrate or a flexible substrate having low heat resistance. In addition, as the above-mentioned peeling layer, for example, a stacked structure of an inorganic film of a tungsten film and a silicon oxide film or a structure in which a resin film such as polyimide is formed on a substrate may be used.

That is, a light-emitting element may be formed using one substrate and then transferred to another substrate. Examples of substrates to which the light-emitting element is transferred include, in addition to the above-mentioned substrates, cellophane substrates, stone substrates, wood substrates, cloth substrates (including natural fibers (silk, cotton, linen), synthetic fibers (nylon, polyurethane, polyester) or recycled fibers (acetate, cuprammonium, rayon, recycled polyester), etc.), leather substrates, rubber substrates, etc. By using these substrates, it is possible to manufacture light-emitting elements that are not easily damaged, light-emitting elements with high heat resistance, light-emitting elements that are lightweight, or light-emitting elements that are thin.

Alternatively, a field effect transistor (FET) may be formed on the substrate, and the light emitting element 150 may be manufactured on an electrode electrically connected to the FET. Thus, an active matrix display device in which the driving of the light emitting element is controlled by the FET may be manufactured.

The structure shown in this embodiment can be used in combination with the structures shown in other embodiments as appropriate.

Embodiment 2 In this embodiment, an example of a method for synthesizing an organic compound of a light-emitting element applicable to an embodiment of the present invention is described by taking an organic compound represented by general formula (G1) and (G2) as an example.

<Method for synthesizing an organic compound represented by general formula (G1)> The organic compound represented by the above general formula (G1) can be synthesized by a synthesis method utilizing various reactions. For example, it can be synthesized by the following synthesis schemes (S-1) and (S-2). By coupling compound 1, arylamine (compound 2) and arylamine (compound 3), a diamine compound (compound 4) is obtained.

Then, by coupling the diamine compound (Compound 4), the halogenated aryl group (Compound 5), and the halogenated aryl group (Compound 6), the organic compound represented by the above general formula (G1) can be obtained.

Note that in the above-mentioned synthesis schemes (S-1) and (S-2), A represents a substituted or unsubstituted fused aromatic ring having 10 to 30 carbon atoms or a substituted or unsubstituted fused heteroaromatic ring having 10 to 30 carbon atoms, ^Ar1 to ^Ar4 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 13 carbon atoms, and ^X1 to ^X8 each independently represent any one of an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 12 carbon atoms. Examples of the fused aromatic ring or fused heteroaromatic ring include chrysene, phenanthrene, stilbene, acridone, phenanthrene, phenanthrene, and phenanthrene. Particularly preferred are anthracene, pyrene, coumarin, quinacridone, perylene, fused tetraphenylene, and naphthobisbenzofuran.

Note that in the above-mentioned synthesis schemes (S-1) and (S-2), when the Buchwald-Hartwig reaction using a palladium catalyst is performed, ^X10 to ^X13 represent a halogen group or a trifluoromethanesulfonate group, and the halogen is preferably iodine, bromine or chlorine. In the above-mentioned reaction, palladium compounds such as bis(dibenzylideneacetone)palladium(0) and palladium(II) acetate, tri(tributyl)phosphine, tri(n-hexyl)phosphine, tricyclohexylphosphine, di(1-adamantane)-n-butylphosphine, and 2-dicyclohexylphosphino-2',6'-dimethoxy-1,1'-biphenyl can be used as ligands. In addition, in the above reaction, organic bases such as sodium tertiary butoxide, inorganic bases such as potassium carbonate, cesium carbonate, sodium carbonate, etc. can be used. As a solvent, toluene, xylene, mesitylene, benzene, tetrahydrofuran, dioxane, etc. can be used. Note that the reagents that can be used in the above reaction are not limited to the above reagents.

The reaction performed in the above-mentioned synthesis schemes (S-1) and (S-2) is not limited to the Buchwald-Hartwig reaction, and the Ueda-Kosugi-Stille coupling reaction using an organotin compound, the coupling reaction using a Grignard reagent, the Ullmann reaction using copper or a copper compound, etc. can also be utilized.

In the above synthesis scheme (S-1), when compound 2 and compound 3 have different structures, it is preferred to react compound 1 with compound 2 to form a coupled product, and then react the obtained coupled product with compound 3. Note that, when compound 1 is reacted with compound 2 and compound 3 one by one, compound 1 is preferably a dihalide, and ^X10 and ^X11 are preferably subjected to amination reaction selectively one by one using different halogens.

Furthermore, in the above synthesis scheme (S-2), when compound 5 and compound 6 have different structures, it is preferred to react compound 4 with compound 5 to form a coupled product, and then react the obtained coupled product with compound 6.

<Method for synthesizing an organic compound represented by general formula (G2)> The organic compound represented by general formula (G2) according to one embodiment of the present invention can be synthesized by various organic reactions. Two methods are shown below as examples.

The first method consists of the following synthesis schemes (S-3) to (S-8). In the initial process, an amine compound (Compound 9) is obtained by a condensation reaction of an aniline compound (Compound 7) and a 1,4-cyclohexadiene-1,4-dicarboxylic acid compound (Compound 8). Synthesis scheme (S-3) shows the process. Note that when two aniline compounds (Compound 7) having the same substituent can be fused in one step to bond the amine group having the same substituent, it is preferred to add 2 equivalent aniline compounds (Compound 7) to carry out the above reaction. At this time, even if the carbonyl group of Compound 8 does not react selectively, the target product can be obtained.

Next, by subjecting the amine compound (Compound 9) and the aniline derivative (Compound 10) to a condensation reaction, a 1,4-cyclohexadiene compound (Compound 11) can be obtained. Synthesis Scheme (S-4) shows the process for obtaining Compound 11.

Next, by oxidizing the 1,4-cyclohexadiene compound (Compound 11) in air, a terephthalic acid compound (Compound 12) can be obtained. Synthesis Scheme (S-5) shows the process for obtaining Compound 12.

Next, the terephthalic acid compound (Compound 12) is condensed with an acid to obtain a quinacridone compound (Compound 13). Synthesis Scheme (S-6) shows the process for obtaining Compound 13.

Next, by coupling the quinacridone compound (Compound 13) and the halogenated aryl group (Compound 14), the quinacridone compound (Compound 15) can be obtained. Synthesis Scheme (S-7) shows the process for obtaining Compound 15. Note that when two halogenated aryl groups (Compound 8) having the same substituent can be coupled in one step to bond to an amine group having the same substituent, it is preferred to add 2 equivalent halogenated aryl groups (Compound 14) to carry out the above reaction. At this time, even if the amine group of Compound 14 does not react selectively, the target product can be obtained.

Next, by coupling the quinacridone compound (Compound 15) and the halogenated aryl group (Compound 16), an organic compound represented by the above general formula (G2) can be obtained. Synthesis Scheme (S-8) shows this process.

The second method consists of synthesis schemes (S-3) to (S-5), and the following (S-9), (S-10) and (S-11). The explanations of (S-3) to (S-5) are as above. By coupling a terephthalic acid compound (compound 12) and a halogenated aryl group (compound 14), a diamine compound (compound 17) can be obtained. Synthesis scheme (S-9) shows the process for obtaining compound 17. Note that when two molecules of halogenated aryl groups having the same substituent can be coupled in one step to bond to an amine group having the same substituent, it is preferred to add 2 equivalent halogenated aryl groups (compound 14) to carry out the above reaction. At this time, even if the amine group of compound 12 does not react selectively, the target product can be obtained.

Next, by coupling the diamine compound (Compound 17) and the halogenated aryl group (Compound 16), a diamine compound (Compound 18) can be obtained. Synthesis Scheme (S-10) shows the process for obtaining Compound 18.

Finally, by condensing the diamine compound (Compound 18) with an acid, an organic compound represented by the general formula (G2) can be obtained. Synthesis Scheme (S-11) shows the process. Note that in the condensation reaction, hydrogen adjacent to Ar ⁵ or Ar ⁶ reacts, and isomers of the organic compound represented by the general formula (G2) may be produced.

In the synthesis scheme (S-11), the organic compound represented by the above general formula (G2) can be synthesized by using a diamine compound (Compound 18) having a symmetrical structure.

In the synthesis schemes (S-3) to (S-6) and (S-9) to (S-11), Al ¹ represents an alkyl group such as a methyl group.

In the synthesis schemes (S-7) to (S-10), ^Y1 and ^Y2 represent chlorine, bromine, iodine, or triflate.

In the synthesis schemes (S-7) to (S-10), it is preferred to perform the Ullmann reaction to carry out the reaction at a high temperature and obtain the target compound in a higher yield. As the reagent that can be used in the reaction, copper or copper compounds, potassium carbonate as a base, sodium hydride and other inorganic bases can be cited. As the solvent that can be used in the reaction, 2,2,6,6-tetramethyl-3,5-heptanedione, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)pyrimidinone (DMPU), toluene, xylene, benzene and the like can be cited. In the Ullmann reaction, when the reaction temperature is 100°C or higher, the target product can be obtained in a shorter time and with a higher yield, so it is preferred to use 2,2,6,6-tetramethyl-3,5-heptanedione, DMPU, and xylene with a higher boiling point. In addition, the reaction temperature is more preferably 150°C or higher, so it is more preferred to use DMPU. The reagents that can be used in this reaction are not limited to the above reagents.

In the synthesis schemes (S-7) to (S-10), a Buchwald-Hartwig reaction using a palladium catalyst can be performed. In this reaction, bis(dibenzylideneacetone)palladium(0), palladium(II) acetate, [1,1-bis(diphenylphosphino)ferrocene]palladium(II)dichloride, tetrakis(triphenylphosphine)palladium(0), allylpalladium(II) chloride dimer, etc. can be used. Ligands such as palladium compounds, tri(tert-butyl)phosphine, tri(n-hexyl)phosphine, tricyclohexylphosphine, di(1-adamantane)-n-butylphosphine, 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl, tri(o-tolyl)phosphine, (S)-(6,6'-dimethoxybiphenyl-2,2'-diyl)bis(diisopropylphosphine) (abbreviation: cBRIDP (registered trademark)) can be used in the reaction. In the reaction, organic bases such as sodium tert-butylate and inorganic bases such as potassium carbonate, cesium carbonate, sodium carbonate and the like can be used. In the reaction, toluene, xylene, benzene, tetrahydrofuran, dioxane and the like can be used as solvents. The reagents that can be used in this reaction are not limited to the above-mentioned reagents.

The method for synthesizing the organic compound represented by the general formula (G2) of the present invention is not limited to the synthesis schemes (S-1) to (S-11).

As specific examples of ^R1 to ^R10 bonded to the quinacridone skeleton, there can be mentioned n-propyl, isopropyl, n-butyl, isobutyl, tertiary butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, trimethylsilyl, triethylsilyl, tributylsilyl and the like.

Specific examples of ^Ar5 to which ^X9 and ^X10 are bonded and ^Ar6 to which ^X11 and ^X12 are bonded include 2-isopropylphenyl, 2-butylphenyl, 2-isobutylphenyl, 2-tert-butylphenyl, 2-isopropylphenyl, 2-butylphenyl, 3-propylphenyl, 3-isobutylphenyl, 3-tert-butylphenyl, 4-propylphenyl, 4-isopropylphenyl, 4-butylphenyl, 4-isobutylphenyl, 4-tert-butylphenyl, 3,5-dipropylphenyl, 3,5-di-isopropylphenyl, 3,5-di-isobutyl ... Propylphenyl, 3,5-dibutylphenyl, 3,5-di-isobutylphenyl, (3,5-di-tert-butyl)phenyl, 1,3-dipropylphenyl, 1,3-di-isopropylphenyl, 1,3-dibutylphenyl, 1,3-di-isobutylphenyl, (1,3-di-tert-butyl)phenyl, 1,3,5-tri-isopropylphenyl, (1,3,5-tri-tert-butyl)phenyl, 4-cyclohexylphenyl, etc.

The above is a description of a method for synthesizing organic compounds represented by the general formula (G1) and the general formula (G2) according to one embodiment of the present invention. However, the present invention is not limited thereto, and the organic compounds may be synthesized using other synthesis methods.

Implementation method 3 In this implementation method, a light-emitting element having a structure different from that of the light-emitting element shown in implementation method 1 is described with reference to FIG. 6. Note that in FIG. 6, the same shading is used for parts having the same functions as those of the element symbols shown in FIG. 1A, and the element symbols are sometimes omitted. In addition, parts having the same functions as those in FIG. 1A are represented by the same element symbols, and their detailed descriptions are sometimes omitted.

<Structural example 2 of light-emitting element> FIG. 6 is a schematic cross-sectional view of the light-emitting element 250.

The light-emitting element 250 shown in FIG6 has a plurality of light-emitting units (light-emitting unit 106 and light-emitting unit 108) between a pair of electrodes (electrode 101 and electrode 102). One of the plurality of light-emitting units preferably has the same structure as the EL layer 100 shown in FIG1A. That is, the light-emitting element 150 shown in FIG1A preferably has one light-emitting unit, and the light-emitting element 250 preferably has a plurality of light-emitting units. Note that in the light-emitting element 250, although the case where the electrode 101 is an anode and the electrode 102 is a cathode is described, the opposite structure may also be adopted as the structure of the light-emitting element 250.

In the light-emitting element 250 shown in FIG6 , the light-emitting unit 106 and the light-emitting unit 108 are stacked, and the charge generation layer 115 is provided between the light-emitting unit 106 and the light-emitting unit 108. In addition, the light-emitting unit 106 and the light-emitting unit 108 may have the same structure or different structures. For example, the light-emitting unit 108 preferably has the same structure as the EL layer 100.

The light emitting element 250 includes the light emitting layer 120 and the light emitting layer 170. The light emitting unit 106 includes a hole injection layer 111, a hole transport layer 112, an electron transport layer 113, and an electron injection layer 114 in addition to the light emitting layer 120. The light emitting unit 108 includes a hole injection layer 116, a hole transport layer 117, an electron transport layer 118, and an electron injection layer 119 in addition to the light emitting layer 170.

In the light-emitting element 250, any one of the light-emitting units 106 and 108 may contain the compound according to one embodiment of the present invention. Note that the light-emitting layer 120 or the light-emitting layer 170 is preferably the layer containing the compound.

The charge generation layer 115 may have a structure in which an acceptor substance serving as an electron acceptor is added to a hole transport material, or a structure in which a donor substance serving as an electron donor is added to an electron transport material. Alternatively, these two structures may be stacked.

When the charge generating layer 115 includes a composite material composed of an organic compound and an acceptor substance, the composite material that can be used for the hole injection layer 111 shown in Embodiment 1 may be used as the composite material. As the organic compound, various compounds such as aromatic amine compounds, carbazole compounds, aromatic hydrocarbons, and high molecular compounds (oligomers, dendrimers, polymers, etc.) may be used. In addition, as the organic compound, it is preferred to use a substance whose hole mobility is greater than 1×10 ^-6 cm ² /Vs. However, any substance other than these may be used as long as the hole transport property is higher than the electron transport property. Since the composite material composed of an organic compound and an acceptor substance has good carrier injection and carrier transport properties, low voltage drive and low current drive can be achieved. Note that when the surface of the anode side of the light-emitting unit contacts the charge generation layer 115, the charge generation layer 115 can also have the function of the hole injection layer or the hole transport layer of the light-emitting unit, so the hole injection layer or the hole transport layer may not be provided in the light-emitting unit. Alternatively, when the surface of the cathode side of the light-emitting unit contacts the charge generation layer 115, the charge generation layer 115 can also have the function of the electron injection layer or the electron transport layer of the light-emitting unit, so the electron injection layer or the electron transport layer may not be provided in the light-emitting unit.

Note that the charge generating layer 115 may also be a stacked structure of a layer of a composite material including an organic compound and an acceptor substance and a layer composed of other materials. For example, a layer of a composite material including an organic compound and an acceptor substance and a layer including a compound selected from electron-donating substances and a compound with high electron transport properties may be combined. Alternatively, a layer of a composite material including an organic compound and an acceptor substance and a layer including a transparent conductive film may be combined.

The charge generation layer 115 sandwiched between the light-emitting cell 106 and the light-emitting cell 108 only needs to have a structure that injects electrons into one light-emitting cell and injects holes into the other light-emitting cell when a voltage is applied between the electrode 101 and the electrode 102. For example, in FIG6 , when a voltage is applied in such a manner that the potential of the electrode 101 is higher than the potential of the electrode 102, the charge generation layer 115 injects electrons into the light-emitting cell 106 and injects holes into the light-emitting cell 108.

From the viewpoint of light extraction efficiency, the charge generation layer 115 preferably has visible light transmittance (specifically, the transmittance of visible light is 40% or more). In addition, the charge generation layer 115 functions even if its conductivity is lower than that of a pair of electrodes (electrode 101 and electrode 102).

By forming the charge generation layer 115 using the above-mentioned material, it is possible to suppress an increase in the driving voltage when light-emitting layers are stacked.

Although FIG6 illustrates a light-emitting element having two light-emitting units, the same structure can be applied to a light-emitting element having three or more light-emitting units stacked. As shown in the light-emitting element 250, by arranging a plurality of light-emitting units between a pair of electrodes in a manner separated by a charge generating layer, a light-emitting element can be realized that can emit light with high brightness while maintaining a low current density and has a longer life. In addition, a light-emitting element with low power consumption can also be realized.

In addition, in each of the above structures, the luminescent colors of the object materials used for the light-emitting unit 106 and the light-emitting unit 108 can be the same or different. When the light-emitting unit 106 and the light-emitting unit 108 include object materials having the function of emitting light of the same color, the light-emitting element 250 becomes a light-emitting element that exhibits high luminescence brightness at a lower current value, so it is preferred. In addition, when the light-emitting unit 106 and the light-emitting unit 108 include object materials having the function of emitting light of different colors from each other, the light-emitting element 250 emits light of multiple colors, so it is preferred. At this time, when multiple light-emitting materials with different luminescent wavelengths are used for one or both of the light-emitting layer 120 and the light-emitting layer 170, light with different luminescent peaks is synthesized, so the emission spectrum of the light-emitting element 250 has at least two maximum values.

The above structure is suitable for obtaining white luminescence. White luminescence can be obtained by making the light from the luminescent layer 120 and the light from the luminescent layer 170 complementary to each other. It is particularly preferred to select the object material in a manner that realizes white luminescence with high color rendering or luminescence with at least red, green, and blue.

It is preferred that the structure of the light-emitting layer 130 shown in Embodiment 1 is used for one or both of the light-emitting layer 120 and the light-emitting layer 170. By adopting this structure, a light-emitting element with good light-emitting efficiency and reliability can be obtained. The guest material included in the light-emitting layer 130 is a fluorescent material. Therefore, by using the structure of the light-emitting layer 130 shown in Embodiment 1 for one or both of the light-emitting layer 120 and the light-emitting layer 170, a light-emitting element with high efficiency and high reliability can be obtained.

In addition, in a light-emitting element in which more than three light-emitting units are stacked, the light-emitting color of the guest material used for each light-emitting unit can be the same or different. In the case where the light-emitting element includes multiple light-emitting units that emit light of the same color, these multiple light-emitting units can emit high-intensity light with a smaller current value. This structure is suitable for adjusting the light-emitting color. It is particularly preferred for use in the case of using guest materials with different light-emitting efficiencies and exhibiting different light-emitting colors. For example, in the case where three light-emitting units are provided, by providing two light-emitting units including a fluorescent material exhibiting the same light-emitting color and one light-emitting unit including a phosphorescent material exhibiting a light-emitting color different from that of the fluorescent material, the light-emitting intensity of the fluorescent luminescence and the phosphorescent luminescence can be adjusted. In other words, the intensity of the luminous color can be adjusted according to the number of light-emitting units.

In the case of using the above-mentioned light-emitting element including two fluorescent light-emitting units and one phosphorescent light-emitting unit, it is preferred that white light emission can be efficiently obtained by using the following light-emitting elements: a light-emitting element including two light-emitting units including blue fluorescent materials and one light-emitting unit including yellow phosphorescent materials; a light-emitting element including two light-emitting units including blue fluorescent materials and one light-emitting unit including red phosphorescent materials and green phosphorescent materials; or a light-emitting element including two light-emitting units including blue fluorescent materials and one light-emitting unit including red phosphorescent materials, yellow phosphorescent materials and green phosphorescent materials. In this way, the light-emitting element and the phosphorescent light-emitting layer of one embodiment of the present invention can be appropriately combined.

In the above-mentioned light-emitting element including two fluorescent light-emitting units and one phosphorescent light-emitting unit, the phosphorescent light-emitting unit can be replaced by a light-emitting unit having the structure of the light-emitting layer 130 described in the above-mentioned embodiment 1. This is because: by using the structure of the light-emitting layer 130 described in the above-mentioned embodiment 1, a fluorescent light-emitting layer having the same light-emitting efficiency as the phosphorescent light-emitting layer can be obtained.

In addition, at least one of the light-emitting layer 120 and the light-emitting layer 170 may be further divided into layers and each layer may contain a different light-emitting material. That is, at least one of the light-emitting layer 120 and the light-emitting layer 170 may be formed of two or more layers. For example, when the light-emitting layer is formed by stacking the first light-emitting layer and the second light-emitting layer in sequence from the hole transport layer side, a material having a hole transport property may be used as the main material of the first light-emitting layer, and a material having an electron transport property may be used as the main material of the second light-emitting layer. In this case, the light-emitting materials contained in the first light-emitting layer and the second light-emitting layer may be the same or different materials. In addition, the luminescent materials included in the first luminescent layer and the second luminescent layer may be materials having the function of emitting light of the same color or materials having the function of emitting light of different colors. By adopting a structure in which a plurality of luminescent materials having the function of emitting light of different colors are used, white luminescence with high color rendering properties composed of three primary colors or four or more luminescent colors can be obtained.

Note that as a guest material for the light-emitting layer of the phosphorescent light-emitting unit described in Embodiment 3, for example, the phosphorescent material shown below can be used.

Examples of phosphorescent materials having a blue or green luminescence peak include tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviated as Ir(mpptz-dmp) ₃ ), tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazole)iridium(III) (abbreviated as Ir(Mptz) ₃ ), tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazole]iridium(III) (abbreviated as Ir(iPrptz-3b) ₃ ), tris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazole] iridium(III) (abbreviated as Ir(iPr5btz) ₃ ), tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazole] iridium(III) (abbreviated as Ir(Mptz1-mp) ₃ ), tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole) iridium(III) (abbreviated as Ir(Prptz1-Me) ₃ ) and other organometallic iridium complexes with a 1H-triazole skeleton; fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole] iridium(III) (abbreviated as: Ir(iPrpmi) ₃ ), tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato] iridium(III) (abbreviated as: Ir(dmpimpt-Me) ₃ ) and other organometallic iridium complexes with an imidazole skeleton; bis[2-(4',6'-difluorophenyl)pyridinium-N,C ^2' ] iridium(III)tetrakis(1-pyrazole)borate (abbreviated as: FIr6), bis[2-(4',6'-difluorophenyl)pyridinium-N,C ^2' ] iridium (III) picolinate (abbreviated as FIrpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinium-N,C ^2' } iridium (III) picolinate (abbreviated as Ir(CF ₃ ppy) ₂ (pic)), bis[2-(4',6'-difluorophenyl)pyridinium-N,C ^2' ]iridium (III) acetylacetone (abbreviated as FIr(acac)) and the like, which are organometallic iridium complexes having phenylpyridine derivatives with electron-withdrawing groups as ligands. Among the above-mentioned phosphorescent materials, organometallic iridium complexes having nitrogen-containing five-membered heterocyclic skeletons such as 4H-triazole skeletons, 1H-triazole skeletons and imidazole skeletons are particularly preferred because they have high triplet excitation energy, good reliability and luminescence efficiency. In addition, platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum (II) (abbreviated as PtOEP) and rare earth metal complexes such as tris[1-(2-thienylcarbonyl)-3,3,3-trifluoroacetone](monophenanthridine)piperidinium (III) (abbreviated as Eu(TTA) ₃ (Phen)) can also be used.

In addition, examples of substances having a luminescence peak in green or yellow include tris(4-methyl-6-phenylpyrimidinyl) iridium(III) (abbreviated as Ir(mppm) ₃ ), tris(4-tert-butyl-6-phenylpyrimidinyl) iridium(III) (abbreviated as Ir(tBuppm) ₃ ), (acetylacetone)bis(6-methyl-4-phenylpyrimidinyl) iridium(III) (abbreviated as Ir(mppm) ₂ (acac)), (acetylacetone)bis(6-tert-butyl-4-phenylpyrimidinyl) iridium(III) (abbreviated as Ir(tBuppm) ₂ (acac)), (acetylacetone)bis(4-(2-norbornyl)-6-phenylpyrimidinyl) iridium(III) (abbreviated as Ir(nbppm) ₂ (acac)), (acetylacetonate)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinyl] iridium(III) (abbreviated as Ir(mpmppm) ₂ (acac)), (acetylacetonate)bis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyridinyl-κN3]phenyl-κC} iridium(III) (abbreviated as Ir(dmppm-dmp) ₂ (acac)), (acetylacetonate)bis(4,6-diphenylpyrimidinyl) iridium(III) (abbreviated as Ir(dppm) ₂ (acac)), etc.; (acetylacetonate)bis(3,5-dimethyl-2-phenylpyrazinyl) iridium(III) (abbreviated as Ir(mppr-Me) ₂ (acac)), (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazino)iridium(III) (abbreviated as Ir(mppr-iPr) ₂ (acac)), etc.; tris(2-phenylpyridino-N,C ^2' )iridium(III) (abbreviated as Ir(ppy) ₃ ), bis(2-phenylpyridino-N,C ^2' )iridium(III) acetylacetonate (abbreviated as Ir(ppy) ₂ (acac)), bis(benzo[h]quinoline)iridium(III) acetylacetonate (abbreviated as Ir(bzq) ₂ (acac)), tris(benzo[h]quinoline)iridium(III) (abbreviated as Ir(bzq) ₃ ), tris(2-phenylquinoline-N,C ^2' )iridium(III) (abbreviated as Ir(pq) ₃ ), bis(2-phenylquinoline-N,C ^2' )iridium(III) acetylacetone (abbreviated as Ir(pq) ₂ (acac)), bis(2,4-diphenyl-1,3-oxazolyl-N,C ^2' )iridium(III) acetylacetone (abbreviated as Ir(dpo) ₂ (acac)), bis{2-[4'-(perfluorophenyl)phenyl]pyridinyl-N,C ^2' }iridium(III) acetylacetone (abbreviated as Ir(p-PF-ph) ₂ (acac)), bis(2-phenylbenzothiazole-N,C ^2' ) iridium (III) acetylacetonate (abbreviated as Ir(bt) ₂ (acac)). In addition, rare earth metal complexes such as tris(acetylacetonate)(monophenanthenate)zirconia (III) (abbreviated as Tb(acac) ₃ (Phen)) can be cited. Among the above complexes, organic metal iridium complexes having a pyrimidine skeleton are particularly preferred because of their excellent reliability and luminescence efficiency.

In addition, examples of substances having a luminescence peak in yellow or red include: (diisobutylenemethano)bis[4,6-bis(3-methylphenyl)pyrimidinyl]iridium(III) (abbreviated as Ir(5mdppm) ₂ (dibm)), bis[4,6-bis(3-methylphenyl)pyrimidinyl](diniopentylmethane)iridium(III) (abbreviated as Ir(5mdppm) ₂ (dpm)), bis[4,6-di(naphthalene-1-yl)pyrimidinyl](diniopentylmethane)iridium(III) (abbreviated as Ir(d1npm) ₂ (dpm)) and other organometallic iridium complexes with a pyrimidine skeleton; (acetylacetonato)bis(2,3,5-triphenylpyrazine) iridium(III) (abbreviated as Ir(tppr) ₂ (acac)), bis(2,3,5-triphenylpyrazine) (diniopentylmethane) iridium(III) (abbreviated as Ir(tppr) ₂ (dpm)), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato] iridium(III) (abbreviated as Ir(Fdpq) ₂ (acac)) and other organometallic iridium complexes with a pyrazine skeleton; tris(1-phenylisoquinoline-N,C ^2' ) iridium(III) (abbreviated as Ir(piq) ₃ ), bis(1-phenylisoquinoline-N,C ^2' )iridium(III) acetylacetonate (abbreviated as: Ir(piq) ₂ (acac)) and other organometallic iridium complexes having a pyridine skeleton. In addition, platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum (II) (abbreviated as PtOEP); rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedione (propanedionato))(monomorphinyl)piperidinium (III) (abbreviated as Eu(DBM) ₃ (Phen)), tris[1-(2-thienylcarbonyl)-3,3,3-trifluoroacetone](monomorphinyl)piperidinium (III) (abbreviated as Eu(TTA) ₃ (Phen)) can be cited. Among the above phosphorescent materials, organometallic iridium complexes having a pyrimidine skeleton are particularly preferred because of their excellent reliability and luminous efficiency. In addition, organometallic iridium complexes with a pyrazine skeleton can obtain red luminescence with good chromaticity.

In addition, as a host material of the phosphorescent light-emitting unit, the above-mentioned hole-transporting material and/or electron-transporting material can be used.

In addition, the fluorescent light-emitting unit may also adopt a structure other than the structure of the light-emitting layer 130 described in Embodiment 1. There is no particular limitation on the guest material used for the fluorescent light-emitting unit. Anthracene derivatives, tetraphenylene derivatives, chrysene derivatives, phenanthrene derivatives, pyrene derivatives, perylene derivatives, stilbene derivatives, acridone derivatives, coumarin derivatives, phenanthrene derivatives, phenanthrene derivatives, etc. are preferably used as fluorescent compounds. For example, the following substances can be used.

Specifically, 5,6-bis[4-(10-phenyl-9-anthracenyl)phenyl]-2,2'-bipyridine (abbreviated as PAP2BPy), 5,6-bis[4'-(10-phenyl-9-anthracenyl)biphenyl-4-yl]-2,2'-bipyridine (abbreviated as PAPP2BPy), N,N'-diphenyl-N,N'-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviated as 1,6FLPAPrn), N,N'-bis(3-methylphenyl)-N,N'-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviated as 1,6mMemFLPAPrn), N,N'-bis[4-(9 -phenyl-9H-fluoren-9-yl)phenyl]-N,N'-bis(4-tributylphenyl)-pyrene-1,6-diamine (abbreviated as: 1,6tBu-FLPAPrn), N,N'-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N'-diphenyl-3,8-dicyclohexylpyrene-1,6-diamine (abbreviated as: ch-1,6FLPAPrn), N,N'-bis[4-(9H-carbazol-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine (abbreviated as: YGA2S), 4-(9H-carbazol-9-yl)-4'-(10-phenyl-9-anthracenyl)triphenylamine (abbreviated as: YGAPA), 4-(9H-carbazol-9-yl)-4 '-(9,10-diphenyl-2-anthracenyl)triphenylamine (abbreviated as: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole-3-amine (abbreviated as: PCAPA), perylene, 2,5,8,11-tetra(tributyl)perylene (abbreviated as: TBP), 4-(10-phenyl-9-anthracenyl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviated as: PCBAPA), N,N''-(2-tributylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N',N'-triphenyl-1,4-phenylene diamine] (abbreviated as: DPABPA), N,9-diphenyl-N-[4-(9,10 -diphenyl-2-anthracenyl)phenyl]-9H-carbazole-3-amine (abbreviated as: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthracenyl)phenyl]-N,N’,N’-triphenyl-1,4-phenylenediamine (abbreviated as: 2DPAPPA), N,N,N’,N’,N’’,N’’,N’’’,N’’’-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine (abbreviated as: DBC1), Coumarin 30, N-(9,10-diphenyl-2-anthracenyl)-N,9-diphenyl-9H-carbazole-3-amine (abbreviated as: 2PCAPA), N-[9,10-bis(1,1’-biphenyl-2-yl)-2-anthracenyl]-N,9-diphenyl- 9H-carbazole-3-amine (abbreviated as: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)-N,N’,N’-triphenyl-1,4-phenylenediamine (abbreviated as: 2DPAPA), N-[9,10-bis(1,1’-biphenyl-2-yl)-2-anthryl]-N,N’,N’-triphenyl-1,4-phenylenediamine (abbreviated as: 2DPABPhA), 9,10-bis(1,1’-biphenyl-2-yl)-N-[4-(9H-carbazole-9-yl)phenyl]-N-phenylanthracen-2-amine (abbreviated as: 2YGABPhA), N,N,9-triphenylanthracen-9-amine (abbreviated as: DPhAPhA), Coumarin 6, Coumarin 545T, N,N’ -diphenylquinacridone (abbreviation: DPQd), red fluorene, 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyl fused tetraphenyl (abbreviation: TBRb), Nile Red, 5,12-bis(1,1'-biphenyl-4-yl)-6,11-diphenyl fused tetraphenyl (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]vinyl}-6-methyl-4H-pyran-4-ylidene)malononitrile (abbreviation: DCM1), 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)vinyl]-4H-pyran-4-ylidene}malononitrile (abbreviation: DCM2), N,N , N’,N’-tetrakis(4-methylphenyl) fused tetraphenyl-5,11-diamine (abbreviated as: p-mPhTD), 7,14-diphenyl-N,N,N’,N’-tetrakis(4-methylphenyl)acenaphtho[1,2-a]propadienylfluorene-3,10-diamine (abbreviated as: p-mPhAFD), 2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)vinyl]-4H-pyran-4-ylidene}malononitrile (abbreviated as: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H -benzo[ij]quinolizin-9-yl)vinyl]-4H-pyran-4-ylidene}malononitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]vinyl}-4H-pyran-4-ylidene)malononitrile (abbreviation: BisDCM), 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-hydro-1H,5H-benzo[ij]quinolizin-9-yl)vinyl]-4H-pyran-4-ylidene}malononitrile (abbreviation: BisDCJTM), 5,10,15,20-tetraphenylbisbenzo[5,6]indeno[1,2,3-cd:1’,2’,3’-lm]perylene (abbreviation: DBP), etc.

In addition, as the guest material of the fluorescent light-emitting unit, the hole transport material and/or the electron transport material mentioned above can be used. This embodiment can be combined with other embodiments as appropriate.

Implementation method 4 In this implementation method, a light-emitting device using the light-emitting element described in implementation methods 1 and 3 is described with reference to FIG. 7A and FIG. 7B.

FIG7A is a top view of the light-emitting device, and FIG7B is a cross-sectional view cut along A-B and C-D in FIG7A. The light-emitting device includes a driving circuit portion (source-side driving circuit) 601 for controlling the light emission of the light-emitting element, a pixel portion 602, and a driving circuit portion (gate-side driving circuit) 603, which are indicated by dotted lines. In addition, component symbol 604 is a sealing substrate, component symbol 625 is a desiccant, component symbol 605 is a sealant, and the inner side surrounded by the sealant 605 is a space 607.

In addition, the guide wiring 608 is used to transmit the signal input to the source side driving circuit 601 and the gate side driving circuit 603, and receives the video signal, clock signal, start signal, reset signal, etc. from the FPC (flexible printed circuit) 609 used as an external input terminal. In addition, although only the FPC is shown here, the FPC can also be installed with a printed wiring board (PWB). The light-emitting device in this specification includes not only the light-emitting device body, but also the light-emitting device installed with the FPC or PWB.

Next, the cross-sectional structure of the light emitting device will be described with reference to Fig. 7B , where a source-side driver circuit 601 as a driver circuit portion and one pixel in a pixel portion 602 are shown.

In addition, in the source side driver circuit 601, a CMOS circuit combining an n-channel TFT 623 and a p-channel TFT 624 is formed. In addition, the driver circuit can also be formed using various CMOS circuits, PMOS circuits, or NMOS circuits. In addition, in the present embodiment, although a driver-integrated type in which the driver circuit is formed on the substrate is shown, this structure does not necessarily have to be adopted, and the driver circuit can also be formed outside instead of being formed on the substrate.

The pixel portion 602 is formed of a pixel including a switching TFT 611, a current control TFT 612, and a first electrode 613 electrically connected to the drain of the current control TFT 612. An insulator 614 is formed to cover an end of the first electrode 613. The insulator 614 can be formed using a positive photosensitive resin film.

In order to improve the coverage of the film formed on the insulator 614, the upper end or the lower end of the insulator 614 is formed into a curved surface having a curvature. For example, when a photosensitive acrylic resin is used as the material of the insulator 614, it is preferred that only the upper end of the insulator 614 has a curved surface. The curvature radius of the curved surface is preferably greater than or equal to 0.2 μm and less than or equal to 0.3 μm. In addition, as the insulator 614, a negative photosensitive material or a positive photosensitive material can be used.

An EL layer 616 and a second electrode 617 are formed on the first electrode 613. Here, as the material of the first electrode 613 serving as an anode, a material having a large work function is preferably used. For example, in addition to a single-layer film such as an ITO film, an indium tin oxide film containing silicon, an indium oxide film containing 2 wt% or more and 20 wt% or less of zinc oxide, a titanium nitride film, a chromium film, a tungsten film, a Zn film, and a Pt film, a stacked film composed of a titanium nitride film and a film containing aluminum as a main component, and a three-layer stacked film composed of a titanium nitride film, a film containing aluminum as a main component, and a titanium nitride film can also be used. Note that when a stacked structure is used, the wiring resistance is also low, good ohmic contact can be obtained, and it can be used as an anode.

The EL layer 616 is formed by various methods such as evaporation using an evaporation mask, inkjet, spin coating, etc. As a material constituting the EL layer 616, a low molecular compound or a high molecular compound (including an oligomer and a dendrimer) may be used.

In addition, as a material of the second electrode 617 formed on the EL layer 616 and used as a cathode, it is preferable to use a material with a small work function (Al, Mg, Li, Ca, or alloys and compounds thereof, MgAg, MgIn, AlLi, etc.). Note that when light generated in the EL layer 616 passes through the second electrode 617, it is preferable to use a stacked layer composed of a metal thin film with a reduced film thickness and a transparent conductive film (ITO, indium oxide containing 2 wt% or more and 20 wt% or less of zinc oxide, indium tin oxide containing silicon, zinc oxide (ZnO), etc.) as the second electrode 617.

In addition, the light-emitting element 618 is formed by the first electrode 613, the EL layer 616, and the second electrode 617. The light-emitting element 618 preferably has the structure shown in Embodiment 1 and Embodiment 2. In addition, the pixel portion includes a plurality of light-emitting elements, and the light-emitting device of this embodiment may include both the light-emitting elements having the structures described in Embodiment 1 and Embodiment 3 and the light-emitting elements having other structures.

Furthermore, by bonding the sealing substrate 604 and the substrate 610 of the light-emitting element together using the sealant 605, the light-emitting element 618 is provided in the space 607 surrounded by the substrate 610, the sealing substrate 604 and the sealant 605. In addition, the space 607 is filled with a filler, and in addition to being filled with an inert gas (nitrogen, argon, etc.), it is sometimes filled with a resin or a dry material, or both a resin and a dry material.

As the sealant 605, epoxy resin or glass powder is preferably used. In addition, these materials are preferably materials that do not allow moisture and oxygen to pass through as much as possible. In addition, as a material for the sealing substrate 604, in addition to a glass substrate and a quartz substrate, a plastic substrate composed of FRP (Fiber Reinforced Plastics), PVF (polyvinyl fluoride), polyester or acrylic resin can also be used.

By the above method, a light-emitting device using the light-emitting element described in Embodiment 1 and Embodiment 3 can be obtained.

<Structural example 1 of light-emitting element> In FIG. 8A and FIG. 8B, an example of a light-emitting device having a light-emitting element emitting white light and a color layer (color filter) is shown as an example of a display device.

8A shows a substrate 1001, a base insulating film 1002, a gate insulating film 1003, gate electrodes 1006, 1007, 1008, a first interlayer insulating film 1020, a second interlayer insulating film 1021, a peripheral portion 1042, a pixel portion 1040, a driving circuit portion 1041, a first electrode 1024W, 1024R, 1024G, 1024B of a light-emitting element, an EL layer 1028, a second electrode 1029 of the light-emitting element, a sealing substrate 1031, a sealant 1032, a red pixel 1044R, a green pixel 1044G, a blue pixel 1044B, a white pixel 1044W, and the like.

In addition, in FIG. 8A and FIG. 8B , color layers (red color layer 1034R, green color layer 1034G, blue color layer 1034B) are provided on a transparent substrate 1033. In addition, a black layer (black matrix) 1035 may also be provided. The transparent substrate 1033 provided with the color layers and the black layer is aligned and fixed on the substrate 1001. In addition, the color layers and the black layer are covered by a covering layer 1036. In addition, FIG. 8A shows a light-emitting layer through which light is transmitted to the outside without passing through the color layers and a light-emitting layer through which light is transmitted to the outside through the color layers of each color. The light that does not pass through the color layers becomes white light and the light that passes through the color layers becomes red light, blue light, and green light, so that an image can be displayed with pixels of four colors.

8B shows an example in which a red color layer 1034R, a green color layer 1034G, and a blue color layer 1034B are formed between the gate insulating film 1003 and the first interlayer insulating film 1020. As shown in FIG8B, the color layers may be provided between the substrate 1001 and the sealing substrate 1031.

In addition, although the light-emitting device described above uses a light-emitting element having a structure in which light is emitted from the substrate 1001 side on which TFTs are formed (bottom emission type), a light-emitting element having a structure in which light is emitted from the sealing substrate 1031 side (top emission type) may also be used.

<Structural example 2 of light-emitting element> Figures 9A and 9B show cross-sectional views of a top-emitting light-emitting device. In this case, a substrate that does not allow light to pass through can be used as the substrate 1001. The process up to the manufacture of the connection electrode connecting the TFT and the anode of the light-emitting element is performed in the same manner as the bottom-emitting light-emitting device. Then, a third interlayer insulating film 1037 is formed in a manner covering the electrode 1022. The insulating film may also have a planarizing function. The third interlayer insulating film 1037 may be formed using the same material as the second interlayer insulating film 1021 or various other materials.

Although the lower electrode 1025W, the lower electrode 1025R, the lower electrode 1025G, and the lower electrode 1025B of the light-emitting element are all anodes here, they can also be cathodes. In addition, in the top emission type light-emitting device shown in Figures 9A and 9B, it is preferred that the lower electrode 1025W, the lower electrode 1025R, the lower electrode 1025G, and the lower electrode 1025B are reflective electrodes. In addition, it is preferred that the second electrode 1029 has the function of emitting light and the function of allowing light to pass. In addition, it is preferred to use a microcavity structure between the second electrode 1029 and the lower electrodes 1025W, 1025R, 1025G, and 1025B to amplify light of a specific wavelength. The structure of the EL layer 1028 is the same as that described in Embodiments 1 and 3, and is an element structure capable of obtaining white light emission.

In FIG8A and FIG8B and FIG9A and FIG9B, a structure of an EL layer capable of obtaining white luminescence may be realized by using a plurality of luminescent layers or a plurality of luminescent units, etc. Note that the structure for obtaining white luminescence is not limited to this.

When the top emission structure shown in FIG. 9A and FIG. 9B is adopted, a sealing substrate 1031 provided with color layers (red color layer 1034R, green color layer 1034G, blue color layer 1034B) can be used for sealing. A black layer (black matrix) 1030 located between pixels can be provided on the sealing substrate 1031. The color layers (red color layer 1034R, green color layer 1034G, blue color layer 1034B) and the black layer (black matrix) can also be covered by a cover layer. In addition, a light-transmitting substrate is used as the sealing substrate 1031.

In addition, although FIG9A shows a structure for full-color display in three colors of red, green, and blue, as shown in FIG9B , full-color display may be performed in four colors of red, green, blue, and white. In addition, the structure for full-color display is not limited to these structures. For example, full-color display may be performed in four colors of red, green, blue, and yellow.

According to one embodiment of the present invention, a light-emitting element uses a fluorescent material as a guest material. Since the fluorescent material has a sharper spectrum than the phosphorescent material, light with high color purity can be obtained. Therefore, by using the light-emitting element in the light-emitting device shown in this embodiment, a light-emitting element with high color reproducibility can be obtained.

Implementation method 5 In this implementation method, an electronic device and a display device according to an implementation method of the present invention are described.

According to one embodiment of the present invention, an electronic device and a display device having a flat surface, high luminous efficiency and high reliability can be manufactured. According to one embodiment of the present invention, an electronic device and a display device having a curved surface, high luminous efficiency and high reliability can be manufactured. In addition, as described above, a luminous element with high color reproducibility can be obtained.

Examples of electronic devices include televisions; desktop or laptop personal computers; displays for computers, etc.; digital cameras; digital video cameras; digital photo frames; mobile phones; portable game consoles; portable information terminals; audio playback devices; and large-scale game consoles such as pinball machines.

The portable information terminal 900 shown in FIG. 10A and FIG. 10B includes a housing 901, a casing 902, a display portion 903, a hinge portion 905, and the like.

The housing 901 and the housing 902 are connected together by a hinge 905. The portable information terminal 900 can be transformed from a folded state (FIG. 10A) to an unfolded state as shown in FIG10B. Thus, the portable terminal 900 has good portability when carried, and has a large display area, so the visibility when in use is high.

The portable information terminal 900 is provided with a flexible display portion 903 across a housing 901 and a housing 902 connected by a hinge portion 905.

The light emitting device manufactured using one embodiment of the present invention can be used for the display unit 903. Thus, a highly reliable portable information terminal can be manufactured.

The display unit 903 can display at least one of document information, still images, and moving images, etc. When the document information is displayed on the display unit 903, the portable information terminal 900 can be used as an electronic book reader.

When the portable information terminal 900 is unfolded, the display portion 903 is maintained in a state with a large radius of curvature. For example, the display portion 903 may be maintained in a manner including a portion bent with a radius of curvature of 1 mm or more and 50 mm or less, preferably 5 mm or more and 30 mm or less. A portion of the display portion 903 is continuously provided with pixels across the housing 901 and the housing 902, thereby enabling curved display.

The display portion 903 is used as a touch panel and can be operated with a finger, a touch pen, or the like.

The display unit 903 is preferably formed of a flexible display. Thus, continuous display can be performed across the housing 901 and the housing 902. In addition, the housing 901 and the housing 902 may be provided with displays respectively.

In order to prevent the angle formed by the housing 901 and the housing 902 from exceeding a predetermined angle when the portable information terminal 900 is unfolded, the hinge part 905 preferably has a locking mechanism. For example, the locking angle (at which the terminal cannot be opened further) is preferably greater than 90° and less than 180°, and typically can be 90°, 120°, 135°, 150°, or 175°, etc. Thus, the convenience, safety, and reliability of the portable information terminal 900 can be improved.

When the hinge portion 905 has the above-described locking mechanism, it is possible to suppress excessive force from being applied to the display portion 903, thereby preventing damage to the display portion 903. Thus, a highly reliable portable information terminal can be realized.

Housing 901 and housing 902 may also include a power button, an operation button, an external connection port, a speaker, a microphone, etc.

Either housing 901 or housing 902 may be provided with a wireless communication module, and data may be sent and received via a computer network such as the Internet, a local area network (LAN), or wireless fidelity (Wi-Fi: a registered trademark).

The portable information terminal 910 shown in FIG. 10C includes a housing 911, a display portion 912, operation buttons 913, an external connection port 914, a speaker 915, a microphone 916, a camera 917, and the like.

The light emitting device manufactured using one embodiment of the present invention can be used for the display unit 912. Thus, the portable information terminal can be manufactured with a high yield.

In the portable information terminal 910, a touch sensor is provided in the display portion 912. By touching the display portion 912 with a finger or a stylus pen, various operations such as making a call and inputting text can be performed.

In addition, by operating the operation button 913, the power can be turned on and off or the type of image displayed on the display portion 912 can be switched. For example, the e-mail writing screen can be switched to the main menu screen.

In addition, by providing a detection device such as a gyroscope sensor or an acceleration sensor inside the portable information terminal 910, the direction (vertical or horizontal) of the portable information terminal 910 can be determined, and the screen display direction of the display unit 912 can be automatically switched. In addition, the screen display direction can also be switched by touching the display unit 912, operating the operation button 913, or using the microphone 916 to input sound.

The portable information terminal 910 has one or more functions selected from a phone, a notebook, an information reading device, etc. Specifically, the portable information terminal 910 can be used as a smart phone. The portable information terminal 910 can execute various applications such as mobile phone, e-mail, article reading and editing, music playback, animation playback, Internet communication, computer games, etc.

10D includes a housing 921, a display portion 922, operation buttons 923, a shutter button 924, etc. In addition, the camera 920 is equipped with a detachable lens 926.

The light emitting device manufactured by one embodiment of the present invention can be used for the display portion 922. Thus, a camera with high reliability can be manufactured.

Here, although the camera 920 has a structure in which the lens 926 can be removed from the housing 921 and exchanged, the lens 926 and the housing 921 may be formed as one body.

The camera 920 can take still images or moving images by pressing the shutter button 924. In addition, the display unit 922 can also have a touch panel function, and the image can be taken by touching the display unit 922.

In addition, camera 920 can also have flash device and viewfinder etc. installed separately.In addition, these components can also be assembled in housing 921.

FIG. 11A is a schematic diagram showing an example of a sweeping robot.

The sweeping robot 5100 includes a display 5101 on the top and multiple cameras 5102, a brush 5103, and an operation button 5104 on the side. Although not shown, tires and a suction port are provided on the bottom of the sweeping robot 5100. In addition, the sweeping robot 5100 also includes various sensors such as infrared sensors, ultrasonic sensors, acceleration sensors, piezoelectric inductors, optical sensors, and gyroscope sensors. In addition, the sweeping robot 5100 includes a wireless communication unit.

The sweeping robot 5100 can walk automatically, detect garbage 5120, and suck the garbage from a suction port on the bottom.

In addition, the sweeping robot 5100 can determine the presence or absence of obstacles such as walls, furniture, or steps by analyzing the image taken by the camera 5102. In addition, when objects such as wiring that may be wrapped around the brush 5103 are detected through image analysis, the rotation of the brush 5103 can be stopped.

The remaining battery power and the amount of garbage attracted can be displayed on the display 5101. In addition, the walking path of the sweeping robot 5100 can also be displayed on the display 5101. In addition, the display 5101 can be a touch panel, and the operation button 5104 can be displayed on the display 5101.

The sweeping robot 5100 can communicate with a portable electronic device 5140 such as a smartphone. The image captured by the camera 5102 can be displayed on the portable electronic device 5140. Therefore, the owner of the sweeping robot 5100 can know the situation of the room when going out. In addition, the display content of the display 5101 can be confirmed using the portable electronic device 5140 such as a smartphone.

A light emitting device according to one embodiment of the present invention can be used in a display 5101.

The robot 2100 shown in FIG. 11B includes a computing device 2110 , an illumination sensor 2101 , a microphone 2102 , an upper camera 2103 , a speaker 2104 , a display 2105 , a lower camera 2106 , an obstacle sensor 2107 , and a moving mechanism 2108 .

The microphone 2102 has a function of detecting the user's voice and surrounding sounds, etc. In addition, the speaker 2104 has a function of emitting sounds. The robot 2100 can communicate with the user using the microphone 2102 and the speaker 2104.

The display 2105 has the function of displaying various information. The robot 2100 can display the information desired by the user on the display 2105. The display 2105 can be equipped with a touch panel. The display 2105 can be a detachable information terminal. By setting the information terminal at a predetermined position of the robot 2100, charging and data transmission and reception can be performed.

The upper camera 2103 and the lower camera 2106 have the function of photographing the surrounding environment of the robot 2100. In addition, the obstacle sensor 2107 can detect the presence or absence of obstacles in front of the robot 2100 when the robot 2100 moves using the moving mechanism 2108. The robot 2100 can recognize the surrounding environment using the upper camera 2103, the lower camera 2106, and the obstacle sensor 2107 and move safely.

A light emitting device of one embodiment of the present invention can be used in a display 2105.

Fig. 11C is a diagram showing an example of a goggle-type display. The goggle-type display includes, for example, a housing 5000, a display portion 5001, a speaker 5003, an LED lamp 5004, an operation key (including a power switch or an operation switch), a connection terminal 5006, a sensor 5007 (which has a function of measuring the following factors: force, displacement, position, velocity, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electricity, radiation, flow, humidity, inclination, vibration, smell or infrared), a microphone 5008, a second display portion 5002, a support portion 5012, an earphone 5013, and the like.

The light emitting device of one embodiment of the present invention can be used in the display portion 5001 and the second display portion 5002.

12A and 12B show a foldable portable information terminal 5150. The foldable portable information terminal 5150 includes a housing 5151, a display area 5152, and a bent portion 5153. FIG12A shows the portable information terminal 5150 in an unfolded state. FIG12B shows the portable information terminal 5150 in a folded state. Although the portable information terminal 5150 has a large display area 5152, by folding the portable information terminal 5150, the portable information terminal 5150 becomes smaller and more portable.

The display area 5152 can be folded into half by the curved portion 5153. The curved portion 5153 is composed of a retractable member and a plurality of supporting members. When folding, the retractable member is stretched so that the curved portion 5153 has a curvature radius of more than 2 mm, preferably more than 5 mm.

In addition, the display area 5152 may also be a touch panel (input/output device) equipped with a touch sensor (input device). The light-emitting element of one embodiment of the present invention may be used for the display area 5152.

This implementation method can be appropriately combined with other implementation methods.

Embodiment 6 In this embodiment, an example of applying a light-emitting element of an embodiment of the present invention to various lighting devices is described with reference to FIG. 13. By using a light-emitting element of an embodiment of the present invention, a lighting device with high light-emitting efficiency and reliability can be manufactured.

By forming a light-emitting element according to an embodiment of the present invention on a flexible substrate, an electronic device or lighting device having a light-emitting area on a curved surface can be realized.

In addition, a light-emitting device to which a light-emitting element according to an embodiment of the present invention is applied can also be applied to automobile lighting, wherein the lighting is provided on a windshield, a ceiling, or the like.

FIG13 is an example of using a light-emitting element in an indoor lighting device 8501. In addition, since the light-emitting element can be large in area, a large-area lighting device can also be formed. In addition, a lighting device 8502 having a curved surface in the light-emitting area can be formed by using a shell having a curved surface. The light-emitting element shown in this embodiment is in the form of a film, so the design of the shell is highly flexible. Therefore, a lighting device that can correspond to various designs can be formed. In addition, a large lighting device 8503 can also be installed on the indoor wall. Touch sensors can also be installed in the lighting device 8501, the lighting device 8502, and the lighting device 8503 to start or turn off the power.

In addition, by using the light emitting element on the surface side of the table, it is possible to provide a lighting device 8504 having the function of a table. In addition, by using the light emitting element on a part of other furniture, it is possible to provide a lighting device having the function of furniture.

As described above, by applying the light emitting element of one embodiment of the present invention, a lighting device and an electronic device can be obtained. Note that the present invention is not limited to the lighting device and the electronic device shown in this embodiment, but can be applied to electronic devices in various fields.

The structure shown in this embodiment can be used in combination with the structures shown in other embodiments as appropriate. Embodiment 1

In this embodiment, a light-emitting element of an embodiment of the present invention and a manufacturing example of a comparative light-emitting element and the characteristics of the light-emitting element are described. The structure of the light-emitting element manufactured in this embodiment is the same as the structure of the light-emitting element shown in FIG. 1A. Tables 1 to 6 show the detailed structure of the element. In Tables 1 to 4, the value represented by _x1 is the value shown in Table 5, and the value represented by _x2 is the value shown in Table 6. In addition, the structures and abbreviations of the compounds used are shown below.

<Manufacturing of light-emitting element> The following is a method for manufacturing the light-emitting element manufactured in this embodiment.

<<Manufacturing of Light-Emitting Elements 2 to 5>> On a glass substrate, an ITSO film with a thickness of 70 nm was formed as an electrode 101. The electrode area of the electrode 101 was 4 mm ² (2 mm×2 mm).

Next, DBT3P-II and molybdenum oxide (MoO ₃ ) were co-evaporated on the electrode 101 at a weight ratio (DBT3P-II:MoO ₃ ) of 1:0.5 and a thickness of 40 nm to form a hole injection layer 111 .

Next, PCCP with a thickness of 20 nm is evaporated on the hole injection layer 111 as the hole transport layer 112 .

Next, mPCCzPTzn-02, PCCP, Ir(mpptz-diBuCNp) ₃ and 2tBu-ptBuDPhA2Anth were co-evaporated on the hole transport layer 112 at a weight ratio (mPCCzPTzn- ₀₂ :PCCP:Ir(mpptz-diBuCNp) 3:2tBu-ptBuDPhA2Anth) of 0.5:0.5:0.1:x ₁ and a thickness of 30 nm to form a light-emitting layer 130. Next, mPCCzPTzn-02, PCCP, Ir(mpptz-diBuCNp) ₃ and 2tBu-ptBuDPhA2Anth were co-evaporated in a weight ratio (mPCCzPTzn-02:PCCP:Ir(mpptz-diBuCNp) ₃ :2tBu-ptBuDPhA2Anth) of 0.8:0.2:0.1:x ₁ and a thickness of 10 nm. In the light-emitting layer 130, Ir(mpptz-diBuCNp) ₃ is a phosphorescent material having a five-membered ring. In addition, 2tBu-ptBuDPhA2Anth is a fluorescent material having a protective group. Note that the value of x ₁ varies depending on each light-emitting element, and Table 5 shows the value of x ₁ in each light-emitting element.

Next, mPCCzPTzn-02 with a thickness of 20 nm and NBPhen with a thickness of 10 nm were sequentially evaporated on the light-emitting layer 130 to form a transport layer 118. Next, LiF with a thickness of 1 nm was evaporated on the electron transport layer 118 as an electron injection layer 119.

Next, aluminum (Al) is formed to a thickness of 200 nm on the electron injection layer 119 as the electrode 102.

Next, in a glove box in a nitrogen atmosphere, a sealing glass substrate is fixed to a glass substrate on which an organic material is formed using a sealing agent for organic EL, thereby sealing light-emitting elements 2 to 5. Specifically, a sealing agent is applied around the organic material formed on the glass substrate, the glass substrate and the glass substrate for sealing are attached, and ultraviolet light with a wavelength of 365 nm is irradiated at 6 J/ ^cm2 , and a heat treatment is performed at 80°C for 1 hour. Light-emitting elements 2 to 5 are obtained through the above process.

《Manufacturing of light-emitting elements 7 to 10, light-emitting elements 12 to 15, light-emitting elements 17 to 19, light-emitting elements 21 to 24, light-emitting elements 26 to 28, light-emitting elements 30 to 33, comparative light-emitting elements 1, 6, 11, 16, 20, 25, 29, and comparative light-emitting elements 34 to 38》 Light-emitting elements 7 to 10, 12 to 15, 17 to 19, 21 to 24, 26 to 28, 30 to 33, comparative light-emitting elements 1, 6, 11, 16, 20, 25, 29, and 34 to 38 are manufactured by vacuum evaporation in the same manner as light-emitting elements 2 to 5 described above. Tables 1 to 4 show the detailed structures of the light-emitting elements, so the detailed manufacturing method is omitted. In addition, Table 5 shows the values represented by _x1 in Tables 1 to 4, and Table 6 shows the values represented by _x2 .

Comparative light-emitting elements 1, 6, 11, 16, 20, 25, 29 and comparative light-emitting element 34 are light-emitting elements that do not include a fluorescent material in the light-emitting layer 130. Therefore, in the light-emitting element, the phosphorescent material included in each light-emitting layer emits light. The above-mentioned light-emitting elements are light-emitting elements in which a phosphorescent material is used as a guest material (energy acceptor) and are shown as comparative examples of light-emitting elements of one embodiment of the present invention in which a phosphorescent material is used as an energy donor.

Light-emitting elements 2 to 5, 7 to 10, 12 to 15, 21 to 24, 26 to 28, and 30 to 33 are light-emitting elements of an embodiment of the present invention. And, each light-emitting layer 130 includes 2tBu-ptBuDPhA2Anth, a fluorescent material having a protective group. Therefore, the light-emitting element emits fluorescent light. In addition, comparative light-emitting elements 35 to 38 are also fluorescent light-emitting elements including 2tBu-ptBuDPhA2Anth, a fluorescent material having a protective group, in the light-emitting layer 130.

In light-emitting elements 2 to 5, Ir(mpptz-diBuCNp) ₃ is used as a phosphorescent material having a five-membered ring. In light-emitting elements 7 to 10, Ir(mpptz-diPrp) ₃ is used as a phosphorescent material having a five-membered ring. In light-emitting elements 12 to 15, Ir(Mptz1-mp) 3 is used as a phosphorescent material having a five-membered ring. In light-emitting elements 17 to 19, Ir(pbi-diBuCNp) ₃ is used as a phosphorescent material having a five-membered ring. In light-emitting elements 20 to 24 _, fac-Ir(pbi-diBup) ₃ is used as a phosphorescent material having a five-membered ring. In light-emitting elements 26 to 28, Ir(pni-diBup) ₂ is used as a phosphorescent material having a five-membered ring. (mdppy), Ir(pni-diBup) ₃ is used as a phosphorescent material having a five-membered ring in light-emitting elements 30 to 33. The phosphorescent material having a five-membered ring is an example of a phosphorescent material having a triazole skeleton or an imidazole skeleton. In addition, Ir(ppy) ₃ which is a phosphorescent material not having a five-membered ring skeleton is used in comparison light-emitting elements 35 to 38, and comparison light-emitting elements 35 to 38 are manufactured for comparison with the element characteristics of the light-emitting element of one embodiment of the present invention.

mPCCzPTzn-02 and PCCP form an excited complex, and 4,6mCzP2Pm and PCCP form an excited complex.

<Characteristics of light-emitting elements> Next, the characteristics of the light-emitting elements 2 to 5, 7 to 10, 12 to 15, 17 to 19, 21 to 24, 26 to 28, 30 to 33, comparison light-emitting elements 1, 6, 11, 16, 20, 25, 29, and 34 to 38 manufactured as described above were measured. A colorimeter (BM-5A manufactured by Topcon Technohouse) was used for the measurement of brightness and CIE chromaticity. A multi-channel spectrometer (PMA-11 manufactured by Hamamatsu Photonics Co., Ltd.) was used for the measurement of electroluminescence spectra.

Figures 14, 16, 18, 20, 22, 24, 26, and 28 respectively show the external quantum efficiency-brightness characteristics of light-emitting element 2 to light-emitting element 5, light-emitting element 7 to light-emitting element 10, light-emitting element 12 to light-emitting element 15, light-emitting element 17 to light-emitting element 19, light-emitting element 21 to light-emitting element 24, light-emitting element 26 to light-emitting element 28, and light-emitting element 30 to light-emitting element 33, comparison light-emitting elements 1, 6, 11, 16, 20, 25, 29, and comparison light-emitting element 34 to comparison light-emitting element 38. 15, 17, 19, 21, 23, 25, 27, and 29 respectively show electroluminescence spectra when a current of 2.5 mA/cm2 is passed through light-emitting elements 2 to 5, light-emitting elements 7 to 10, light-emitting elements 12 to 15, light-emitting elements 17 to 19, light-emitting elements 21 to 24, light-emitting elements 26 to 28, light-emitting elements 30 to 33, comparative light-emitting elements 1, 6, 11, 16, 20, 25, ²⁹ , and comparative light-emitting elements 34 to 38. Note that the measurement of each light-emitting element was performed at room temperature (an atmosphere maintained at 23°C).

In addition, Tables 7 and 8 show the element characteristics of light-emitting element ² to light-emitting element 5, light-emitting element 7 to light-emitting element 10, light-emitting element 12 to light-emitting element 15, light-emitting element 17 to light-emitting element 19, light-emitting element 21 to light-emitting element 24, light-emitting element 26 to light-emitting element 28 and light-emitting element 30 to light-emitting element 33, comparison light-emitting elements 1, 6, 11, 16, 20, 25, 29 and comparison light-emitting element 34 to comparison light-emitting element 38 near 1000 cd/m2.

<Energy transfer from energy donor (phosphorescent material with five-membered ring skeleton) to energy acceptor (fluorescent material with protective group)> As shown in FIG15, the peak wavelength of the emission spectrum of light-emitting element 2 to light-emitting element 5 is about 528nm and the half width is about 62nm, showing green light originating from 2tBu-ptBuDPhA2Anth. On the other hand, the peak wavelength of the emission spectrum of comparison light-emitting element 1 is 492nm and the half width is 67nm, showing light originating from Ir(mpptz-diBuCNp) _3. Therefore, it can be seen that: in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

As shown in FIG17 , the peak wavelength of the emission spectrum of light-emitting element 7 to light-emitting element 10 is about 530 nm and the half width is about 66 nm, showing green light originating from 2tBu-ptBuDPhA2Anth. On the other hand, the peak wavelength of the emission spectrum of comparison light-emitting element 6 is 508 nm and the half width is 85 nm, showing light originating from Ir(mpptz-diPrp) _3. Therefore, it can be seen that in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

As shown in FIG19 , the peak wavelength of the emission spectrum of the light-emitting element 12 to the light-emitting element 15 is about 529 nm and the half width is about 64 nm, showing green light originating from 2tBu-ptBuDPhA2Anth. On the other hand, the peak wavelength of the emission spectrum of the comparison light-emitting element 11 is 502 nm and the half width is 91 nm, showing light originating from Ir(Mptz1-mp) _3. Therefore, it can be seen that in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

As shown in FIG21 , the emission spectrum of the comparison light-emitting element 16 has a maximum peak wavelength of 513 nm and a half-width of 64 nm, showing light emission from Ir(pbi-diBuCNp) _3. The emission spectrum of the light-emitting element 17 is different from the emission spectrum of the comparison light-emitting element 16. This is because light emission from Ir(pbi-diBuCNp) ₃ and light emission from 2tBu-ptBuDPhA2Anth are detected. Therefore, it can be seen that fluorescent light emission is obtained from the light-emitting element 17. In addition, the emission spectrums of the light-emitting elements 18 and 19 have a peak wavelength of about 535 nm and a half-width of about 69 nm, showing green light emission from 2tBu-ptBuDPhA2Anth. Therefore, it can be understood that in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

As shown in FIG23, the emission spectrum of the comparison light-emitting element 20 has a maximum peak wavelength of 508 nm and a half-width of 64 nm, showing light emission from fac-Ir(pbi-diBup) _3. The emission spectrum of the light-emitting element 21 is different from the emission spectrum of the comparison light-emitting element 20. This is because light emission from fac-Ir(pbi-diBup) ₃ and light emission from 2tBu-ptBuDPhA2Anth are detected. Therefore, it can be seen that fluorescent light is obtained from the light-emitting element 21. In addition, the emission spectrums of the light-emitting elements 22 and 24 have a peak wavelength of about 538 nm and a half-width of about 69 nm, showing green light emission from 2tBu-ptBuDPhA2Anth. Therefore, it can be understood that in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

As shown in FIG25 , the emission spectrum of the comparative light-emitting element 25 has a maximum peak wavelength of 525 nm and a half width of 73 nm, showing light emission from Ir(pni-diBup) ₂ (mdppy). The emission spectrum of the light-emitting element 26 is different from the emission spectrum of the comparative light-emitting element 25. This is because light emission from Ir(pni-diBup) ₂ (mdppy) and light emission from 2tBu-ptBuDPhA2Anth are detected. Therefore, it can be seen that fluorescent light emission is obtained from the light-emitting element 26. In addition, the emission spectrums of the light-emitting elements 27 and 28 have a peak wavelength of about 535 nm and a half width of about 69 nm, showing green light emission from 2tBu-ptBuDPhA2Anth. Therefore, it can be understood that in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

As shown in FIG27 , the emission spectrum of the comparative light-emitting element 29 has a maximum peak wavelength of 500 nm and a half-width of 59 nm, showing light emission from Ir(pni-diBup) _3. The emission spectrum of the light-emitting element 30 is different from the emission spectrum of the comparative light-emitting element 29. This is because light emission from Ir(pni-diBup) ₃ and light emission from 2tBu-ptBuDPhA2Anth are detected. Therefore, it can be seen that fluorescent light emission is obtained from the light-emitting element 29. In addition, the emission spectrums of the light-emitting elements 31 to 33 have a peak wavelength of about 536 nm and a half-width of about 65 nm, showing green light emission from 2tBu-ptBuDPhA2Anth. Therefore, it can be understood that in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

As shown in Fig. 29, the emission spectrum of comparative luminescent element 34 has a maximum peak wavelength of 517 nm and a half width of 70 nm, showing luminescence originating from Ir(ppy) _3. In addition, the emission spectrum of comparative luminescent element 35 to comparative luminescent element 38 has a peak wavelength of about 535 nm and a half width of about 69 nm, showing green luminescence originating from 2tBu-ptBuDPhA2Anth.

Light-emitting elements 2 to 5, 7 to 10, 12 to 15, 17 to 19, 21 to 24, 26 to 28 and 30 to 33 exhibit luminescence originating from the fluorescent material, but as shown in FIGS. 16 , 18 , 20 , 22 , 24 , 26 , Tables 7 and 8, the light-emitting elements having a high concentration of 2tBu-ptBuDPhA2Anth of the fluorescent material also exhibit high luminescence efficiency, that is, an external quantum efficiency of at least more than 14%. In addition, the light-emitting elements 2 to 5, 7 to 10, 12 to 15, 17 to 19, 21 to 24, 26 to 28 and 30 to 33 of the light-emitting elements of an embodiment of the present invention also exhibit an external quantum efficiency higher than that of the comparison light-emitting element 37 at any concentration.

The maximum probability of generating a singlet exciton generated by the recombination of carriers (holes and electrons) injected from a pair of electrodes is 25%, so when the light extraction efficiency to the outside is 30%, the external quantum efficiency of the fluorescent light-emitting element is 7.5% at most. However, high efficiency, that is, an external quantum efficiency higher than 7.5%, is obtained in light-emitting element 2 to light-emitting element 5, light-emitting element 7 to light-emitting element 10, light-emitting element 12 to light-emitting element 15, light-emitting element 21 to light-emitting element 24, light-emitting element 26 to light-emitting element 28, and light-emitting element 30 to light-emitting element 33. This is because: in addition to the luminescence derived from the singlet exciton generated by the recombination of carriers (holes and electrons) injected from a pair of electrodes, luminescence derived from the energy transfer of triplet excitons is also obtained from the fluorescent material. Based on the present results, it can be said that in a light-emitting element of an embodiment of the present invention, by using a fluorescent material having a protecting group and a phosphorescent material having a five-membered ring skeleton, the non-radiative deactivation of triplet excitons is suppressed, and the singlet excitation energy and triplet excitation energy generated in the light-emitting layer are efficiently converted into luminescence of the fluorescent material.

<Overlap of the absorption spectrum of the fluorescent material and the emission spectrum of the phosphorescent material having a five-membered ring> Next, the relationship between the absorption spectrum of the fluorescent material 2tBu-ptBuDPhA2Anth and the EL emission spectrum of the phosphorescent material used in each light-emitting element was investigated. The results are shown in Figures 30 to 36.

As described above, the comparison light-emitting elements 1, 6, 11, 16, 20, 25, and 29 show light emission from the phosphorescent materials used in each light-emitting layer. From Figures 30 to 36, it can be seen that the emission spectrum of each phosphorescent material and the absorption spectrum of 2tBu-ptBuDPhA2Anth have overlapping parts. Therefore, when each phosphorescent material and 2tBu-ptBuDPhA2Anth are used as the light-emitting layer, energy transfer from each phosphorescent material to 2tBu-ptBuDPhA2Anth may occur. Here, as described above, the light-emitting element of an embodiment of the present invention shows high light-emitting efficiency. That is, it can be seen that the deactivation of triplet excitons in the light-emitting layer that occurs in a general fluorescent element is suppressed. This is an effect brought about by the use of a fluorescent material having a protecting group. In addition, the following factors also contribute to the effect: by using a phosphorescent material having a five-membered ring, the recombination of carriers in the fluorescent material is suppressed, and the energy transfer of triplet excitons from the phosphorescent material to the fluorescent material based on the Dexter mechanism and the energy deactivation of triplet excitons are suppressed.

<Changes in external quantum efficiency caused by guest material concentration> FIG. 37 shows the relationship between guest material concentration and external quantum efficiency in light-emitting elements using various phosphorescent materials. As can be seen from FIG. 37, compared with comparative light-emitting elements 34 to 38 using Ir(ppy) ₃ , a phosphorescent material not having a five-membered ring skeleton, the light-emitting element of one embodiment of the present invention using a phosphorescent material having a five-membered ring suppresses the decrease in external quantum efficiency caused by an increase in the concentration of the phosphorescent material. This is because: by using a guest material having a protective group for the light-emitting layer and using a phosphorescent material having a five-membered ring, the energy transfer of triplet excitation energy based on the Dexter mechanism from the host material to the guest material is suppressed and the triplet excitation energy is deactivated. Furthermore, since the energy transfer from the host material to the guest material based on the Förster mechanism can be efficiently utilized by increasing the concentration of the guest material, and the triplet excitation energy and the singlet excitation energy in the luminescent layer can be efficiently converted into the luminescence of the fluorescent material, it can be seen that a light-emitting element with a high concentration of the guest material and high luminescence efficiency can be obtained by a light-emitting element of an embodiment of the present invention.

In addition, it is also known that in the light-emitting element using Ir(mpptz-diPrp) ₃ and Ir(Mptz1-mp) ₃ , the light-emitting efficiency is improved by increasing the concentration of the guest material.

<Reliability measurement of light-emitting elements> Next, a constant current drive test at 2.0 mA was performed on light-emitting elements 2 to 5, light-emitting elements 7 to 10, light-emitting elements 12 to 15, light-emitting elements 17 to 19, light-emitting elements 21 to 24, light-emitting elements 26 to 28, and light-emitting elements 30 to 33, as well as comparison light-emitting elements 1, 6, 11, 16, 20, 25, and 29. The results are shown in Figures 38 to 44. It can be seen from Figures 38 to 44 that reliability is improved by increasing the concentration of the guest material. This means that by increasing the concentration of the guest material, the excitation energy in the light-emitting layer can be efficiently converted into the luminescence of the guest material. In other words, it means that by increasing the concentration of the guest material, the energy transfer rate of the triplet excitation energy from the host material to the guest material based on the Förster mechanism can be increased.

Here, in the light-emitting layer, the energy transfer from the energy donor to the guest material, that is, the energy transfer associated with the light emission, competes with the quenching process caused by the influence of impurities or deterioration products. Therefore, in order to obtain a light-emitting element with good reliability, it is important to increase the energy transfer speed associated with the light emission.

<Measurement of fluorescence lifetime of light-emitting elements> Next, in order to investigate the difference in light emission speed caused by the difference in the concentration of the object material, the fluorescence lifetime of light-emitting elements 2 to 5, light-emitting elements 7 to 10, light-emitting elements 12 to 15, and light-emitting elements 1, 6, and 11 were measured. In the measurement, a picosecond fluorescence lifetime measurement system (manufactured by Hamamatsu Photonics Co., Ltd., Japan) was used. In this measurement, in order to measure the lifetime of the fluorescent light emission in the light-emitting element, a rectangular pulse voltage was applied to the light-emitting element, and the light emission that decayed after the voltage dropped was time-resolved measured using a streak camera. The pulse voltage is applied at a frequency of 10 Hz, and data with a high S/N ratio are obtained by accumulating the data of repeated measurements. In addition, the test is carried out under the following conditions: at room temperature (300K), an applied pulse voltage of about 3V to 4V is applied in such a way that the brightness of the light-emitting element is around 1000cd/ ^m2 , the applied pulse time width is 100μsec, the negative bias voltage is -5V (when the element drive is OFF), and the measurement time range is 10μsec. Figures 49 to 51 show the measurement results. Note that in Figures 49 to 51, the vertical axis represents the normalized intensity of the luminescence intensity in the state of continuous carrier injection (when the pulse voltage is ON). In addition, the horizontal axis represents the time after the pulse voltage drops.

By fitting the decay curves shown in FIGS. 49 to 51 with an exponential function, it can be seen that: light-emitting elements 2 to 5, and light-emitting elements 7 to 10 emit light having an instantaneous fluorescence component of less than 0.4 μs and a delayed fluorescence component of about 2 μs, and light-emitting elements 12 to 15 emit light having an instantaneous fluorescence component of less than 0.4 μs and a delayed fluorescence component of about 4 μs. In addition, it can be seen that: when a fluorescent material is added as a guest material, the higher the concentration of the fluorescent material, the higher the proportion of the instantaneous fluorescence component and the lower the proportion of the delayed fluorescence component. In addition, it can be seen that: the comparison luminescent element 1 exhibits luminescence originating from the phosphorescent material and exhibits luminescence having an instantaneous fluorescent component of less than 0.5 μ second and a delayed fluorescent component of about 4 μ second, and the comparison luminescent element 6 and the comparison luminescent element 11 exhibit luminescence originating from the phosphorescent material and exhibits luminescence having an instantaneous fluorescent component of less than 0.5 μ second and a delayed fluorescent component of about 2 μ second.

It can be seen that by adding the fluorescent material as the guest material to the light-emitting layer, the light-emitting speed is improved and the proportion of the instantaneous fluorescent component originating from the fluorescent material is increased. Here, as described above, the light-emitting element 2 to the light-emitting element 5, the light-emitting element 7 to the light-emitting element 10, and the light-emitting element 12 to the light-emitting element 15 of an embodiment of the present invention show high external quantum efficiency even if the concentration of the fluorescent material is high. That is, it can be seen that in the light-emitting element of an embodiment of the present invention, even if the proportion of light emission originating from the fluorescent material increases, it still shows high light-emitting efficiency. This means: in the light-emitting element of an embodiment of the present invention, the energy transfer of the triplet excitation energy based on the Dexter mechanism from the host material to the guest material and the deactivation of the triplet excitation energy can be suppressed, and the concentration of the guest material can be increased, so that the energy transfer efficiency of the excitation energy based on the Foster mechanism can be improved. Therefore, in the light-emitting element of one embodiment of the present invention, both singlet excitation energy and triplet excitation energy can be efficiently used for light emission.

In addition, as shown in Figures 49 to 51, in order to increase the energy transfer rate, it is better to increase the concentration of the guest material in the light-emitting layer. The light-emitting element of an embodiment of the present invention can suppress the energy transfer based on the Dexter mechanism and increase the energy transfer rate based on the Foster mechanism. By reducing the impact of the competition with the quenching process, a light-emitting element with good luminous efficiency and good reliability can be obtained. In addition, phosphorescence is observed in each comparative light-emitting element, so the luminescence life is long, but the light-emitting element of an embodiment of the present invention is fluorescent, so the luminescence life is short. Therefore, the impact of the competition with the above-mentioned quenching process can be reduced. Therefore, in a light-emitting element of an embodiment of the present invention, the concentration of the object material can be increased, and a light-emitting element with high light-emitting efficiency and reliability can be obtained. Example 2

In this embodiment, a light-emitting element of an embodiment of the present invention different from Embodiment 1 and a manufacturing example of a comparative light-emitting element and the characteristics of the light-emitting element are described. The structure of the light-emitting element manufactured in this embodiment is the same as the structure of the light-emitting element shown in FIG. 1A. Table 9 shows the detailed structure of the element. In addition, the structure and abbreviation of the compound used are shown below. For other organic compounds, reference can be made to the above-mentioned embodiments and the above-mentioned embodiments.

<<Manufacturing of Comparative Light-Emitting Element 39 and Light-Emitting Element 40 to Light-Emitting Element 43>> Similar to the above-mentioned Light-Emitting Element 2 to Light-Emitting Element 5, Comparative Light-Emitting Element 39 and Light-Emitting Element 40 to Light-Emitting Element 43 are manufactured by vacuum evaporation. Tables 9 and 10 show the detailed structure of each light-emitting element, so the detailed manufacturing method is omitted. In addition, Table 10 shows the value represented by x ₃ in Table 9.

In the comparative light-emitting element 39, Ir(pbi-diBuCNp) ₃ of the phosphorescent material is used as an energy acceptor. The comparative light-emitting element 39 is shown as a comparative example of a light-emitting element of one embodiment of the present invention in which a phosphorescent material is used as an energy donor.

<Characteristics of light-emitting elements> Next, the characteristics of the comparison light-emitting element 39 and the light-emitting elements 40 to 43 manufactured as described above were measured. The measurement method was the same as that of Example 1.

FIG52 shows the external quantum efficiency-luminance characteristics of the comparative light-emitting element 39 and the light-emitting elements 40 to 43. FIG53 shows the electroluminescence spectrum when a current of 2.5 mA/ ^cm2 is passed through the comparative light-emitting element 39 and the comparative light-emitting element 40 to 43. Note that the measurement of each light-emitting element was performed at room temperature (an atmosphere maintained at 23°C).

Table 11 shows the device characteristics of the comparative light emitting element 39 and the comparative light emitting elements 40 to 43 at around 1000 cd/m ² .

<Energy transfer from energy donor (phosphorescent material with five-membered ring skeleton) to energy acceptor (fluorescent material with protective group)> As shown in FIG. 53, the peak wavelength of the emission spectrum of light-emitting element 40 to light-emitting element 43 is about 520nm and the half width is about 69nm, showing green light originating from 2,6tBu-mmtBuDPhA2Anth. On the other hand, the peak wavelength of the emission spectrum of comparison light-emitting element 39 is 513nm and the half width is 63nm, showing light originating from Ir(pbi-diBuCNp) _3. Therefore, it can be seen that: in the light-emitting element of one embodiment of the present invention, energy is transferred from the phosphorescent material to the fluorescent material.

Although the light-emitting elements 40 to 43 exhibit light emission from the fluorescent material, as shown in FIG. 52 and Table 11, the light-emitting elements having a high concentration of the fluorescent material also exhibit high light emission efficiency, that is, an external quantum efficiency of at least more than 15%. Based on this result, it can be said that in the light-emitting element of one embodiment of the present invention, by using a fluorescent material having a protective group and a phosphorescent material having a five-membered ring skeleton, the singlet excitation energy and triplet excitation energy generated in the light-emitting layer are efficiently converted into light emission of the fluorescent material by suppressing the non-radiative deactivation of triplet excitons.

<Reliability measurement of light-emitting element> Next, a constant current drive test at 2.0 mA was performed to compare light-emitting element 39 and light-emitting element 40 to light-emitting element 43. The results are shown in FIG54. As can be seen from FIG54, reliability is improved by increasing the concentration of the guest material. This means that by increasing the concentration of the guest material, the excitation energy in the light-emitting layer can be efficiently converted into the luminescence of the guest material. In other words, by increasing the concentration of the guest material, the energy transfer rate of the triple excitation energy based on the Förster mechanism from the host material to the guest material can be increased.

<Measurement of fluorescence life of light-emitting element> Next, in order to investigate the difference in light emission speed caused by the difference in the concentration of the object material, the fluorescence life of light-emitting element 39 and light-emitting element 40 to light-emitting element 43 was measured and compared. The measurement method was the same as that of Example 1. The results are shown in FIG55.

As can be seen from FIG55, the higher the concentration of the fluorescent material (guest material), the higher the proportion of the fluorescent component with a fast luminescence speed and the lower the proportion of the delayed fluorescent component. It can be seen that by adding the fluorescent material as the guest material to the luminescent layer, the luminescence speed is increased and the proportion of the instantaneous fluorescent component originating from the fluorescent material is increased.

Here, as described above, even when a light-emitting element having a high concentration of fluorescent material is used, the light-emitting elements 40 to 43 of one embodiment of the present invention exhibit high external quantum efficiency. That is, it can be seen that in the light-emitting element of one embodiment of the present invention, even if the proportion of luminescence originating from the fluorescent material increases, high luminescence efficiency is exhibited. This means that: in the light-emitting element of one embodiment of the present invention, the energy transfer of triplet excitation energy based on the Dexter mechanism from the host material to the guest material and the deactivation of triplet excitation energy can be suppressed, and the concentration of the guest material can be increased, thereby improving the energy transfer efficiency of the excitation energy based on the Foster mechanism. Therefore, in the light-emitting element of one embodiment of the present invention, both singlet excitation energy and triplet excitation energy can be efficiently used for luminescence.

(Reference Example 1) This reference example describes the synthesis method of the fluorescent material with a protective group used in Example 1, namely 2tBu-ptBuDPhA2Anth.

1.2 g (3.1 mmol) of 2-tert-butylanthracene, 1.8 g (6.4 mmol) of bis(4-tert-butylphenyl)amine, 1.2 g (13 mmol) of sodium tert-butoxide, and 60 mg (0.15 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxy-1,1'-biphenyl (abbreviated as: SPhos) were placed in a 200 mL three-necked flask, and the air in the flask was replaced with nitrogen. 35 mL of mesitylene was added to the mixture, and the mixture was degassed under reduced pressure. 40 mg (70 μmol) of bis(dibenzylideneacetone)palladium(0) was added to the mixture, and then the mixture was stirred at 170°C for 4 hours under a nitrogen flow.

After stirring, 400 mL of toluene was added to the obtained mixture, and then the mixture was filtered by suction through magnesium silicate (Wako Pure Chemical Industries, Ltd., catalog number: 066-05265), diatomaceous earth (Wako Pure Chemical Industries, Ltd., catalog number: 537-02305), and alum to obtain a filtrate. The obtained filtrate was concentrated to obtain a brown solid.

The solid was purified by silica gel column chromatography (developing solvent: hexane: toluene = 9:1) to obtain the target yellow solid. The yellow solid was recombined with toluene, hexane and ethanol to obtain 1.5 g of the target yellow solid with a yield of 61%. The synthesis scheme (A-1) is shown below.

1.5 g of the obtained yellow solid was purified by gradient sublimation. The yellow solid was heated at 315°C for 15 hours under a pressure of 4.5 Pa for sublimation purification. After sublimation purification, 1.3 g of the target yellow solid was obtained at a recovery rate of 89%.

In addition, the measurement results of the yellow solid obtained by this synthesis using ¹ H-NMR are shown below. In addition, Figures 45A, 45B and 46 show ¹ H-NMR spectra. Figure 45B is an enlarged view of the range of 6.5ppm to 9.0ppm of Figure 45A. In addition, Figure 46 is an enlarged view of the range of 0.5ppm to 2.0ppm of Figure 45A. From this result, it can be seen that the target 2tBu-ptBuDPhA2Anth is obtained.

¹ H-NMR (CDCl ₃ , 300MHz): σ=8.20-8.13 (m, 2H), 8.12 (d, J=8.8Hz, 1H), 8.05 (d, J=2.0Hz, 1H), 7.42 (dd, J=9.3Hz, 2.0Hz, 1H), 7.32-7.26 (m, 2H) 7.20 (d, J=8.8Hz, 8H), 7.04 (dd, J=8.8Hz, 2.4Hz, 8H), 1.26 (s, 36H), 1.18 (s, 9H).

(Reference Example 2) In this reference example, a method for synthesizing Ir(pni-diBup) ₃ , which is an example of a phosphorescent material having a five-membered ring used in Example 1, is described.

<Step 1: Synthesis of 2,6-diisobutylaniline> 100 g (617 mmol) of 2,6-dichloroaniline, 230 g (2256 mmol) of isobutylboric acid, 479 g (2256 mmol) of tripotassium phosphate, 10 g (24.7 mmol) of 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (S-phos), and 3000 mL of toluene were placed in a 5000 mL three-necked flask, the air in the flask was replaced with nitrogen, and the mixture was degassed while being stirred while reducing the pressure in the flask. After degassing, 11 g (11.5 mmol) of tris(dibenzylideneacetone)dipalladium (0) was added, and the mixture was stirred at 120°C for 12 hours under a nitrogen flow. After a predetermined time, the obtained reaction solution was subjected to suction filtration. The obtained reaction solution was purified by extraction with toluene. Then, it was purified by silica gel column chromatography. As a developing solvent, hexane: toluene = 15: 1 was used. The obtained distillate was concentrated to obtain 79 g of a black oily substance of the target substance at a yield of 62%. The following formula (B-1) shows the synthesis scheme of step 1.

<Step 2; Synthesis of 2-nitronaphthalene-1-trifluoromethanesulfonate> 35 g (182 mmol) of 2-nitro-1-naphthol, 500 mL of dehydrated dichloromethane, and 51 mL (365 mmol) of triethylamine were placed in a 1000 mL three-necked flask, the air in the flask was replaced with nitrogen, and the temperature was cooled to 0°C. 40 mL (243 mmol) of trifluoromethanesulfonic anhydride (abbreviated as: Tf ₂ O) was added dropwise, and the mixture was stirred at 0°C for 1 hour and at room temperature for 20 hours. After a specified time, 300 mL of water and 30 mL of 1M hydrochloric acid were added to the obtained mixture. Then, the mixture was purified by extraction using dichloromethane. Then, the mixture was purified by silica gel column chromatography. As a developing solvent, hexane: dichloromethane = 5:1 was used. The obtained distillation fraction was concentrated to obtain 47 g of the target compound as a yellow oil with a yield of 80%. The following formula (B-2) shows the synthesis scheme of step 2.

<Step 3; Synthesis of N-(2,6-diisobutylphenyl)-2-nitro-1-naphthylamine> Put 30 g (146 mmol) of 2,6-diisobutylaniline synthesized in step 1, 47 g (146 mmol) of 2-nitronaphthalene-1-trifluoromethanesulfonate synthesized in step 2, 81 g (248 mmol) of cesium carbonate, and 750 mL of toluene in a 2000 mL three-necked flask, replace the air in the flask with nitrogen, and depressurize the flask while stirring to degas the mixture. After degassing, add S-phos 4.8g (11.7mmol) and tris(dibenzylideneacetone)dipalladium (0) 2.7g (2.9mmol), and stir at 130°C for 28 hours under a nitrogen flow. After the specified time, the obtained mixture is purified by extraction using toluene. Then, it is purified by silica gel column chromatography. As a developing solvent, hexane: ethyl acetate = 15:1 is used. The obtained distillate is concentrated to obtain 13g of a yellow oily substance at a yield of 23%. The following formula (B-3) shows the synthesis scheme of step 3.

<Step 4; Synthesis of N-(2,6-diisobutylphenyl)-1,2-naphthalenediamine> Put 13 g (34 mmol) of N-(2,6-diisobutylphenyl)-2-nitro-1-naphthylamine synthesized in Step 3, 6.1 mL (0.34 mol) of water, and 400 mL of ethanol in a 1000 mL three-necked flask and stir. Add 32 g (0.17 mol) of tin (II) chloride to the mixture, and stir at 80°C for 5 hours under a nitrogen flow. After a specified time, pour the obtained reaction mixture into 500 mL of a 2M sodium hydroxide aqueous solution and stir at room temperature for 2 hours. The precipitate is filtered by suction and washed with chloroform to obtain a filtrate. The obtained filtrate was purified by extraction with chloroform. Then, it was purified by silica gel column chromatography. As a developing solvent, hexane:ethyl acetate = 15:1 was used. The obtained distillate was concentrated to obtain 9.5 g of the target black oily substance with a yield of 81%. The following formula (B-4) shows the synthesis scheme of step 4.

<Step 5; Synthesis of 1-(2,6-diisobutylphenyl)-2-phenyl-1H-naphtho[1,2-d]imidazole (abbreviated as: Hpni-diBup)> 9.5 g (27 mmol) of N-(2,6-diisobutylphenyl)-1,2-naphthalenediamine synthesized in Step 4, 100 mL of acetonitrile, and 2.9 g (27 mmol) of benzaldehyde were placed in a 300 mL eggplant-shaped flask and stirred at 100°C for 6 hours. 0.044 g (0.274 mmol) of iron (III) chloride was added to the mixture and stirred at 100°C for 16 hours. After the specified time, the obtained reaction mixture was extracted with ethyl acetate, and 100 mL of toluene and 10 g of manganese (IV) oxide were added to the obtained oily substance, and the mixture was placed in a 300 mL eggplant-shaped flask and stirred at 130°C for 7 hours. After the specified time, the obtained reaction mixture was suction filtered through diatomaceous earth (Wako Pure Chemical Industries, Ltd., catalog number: 537-02305)/magnesium silicate (Wako Pure Chemical Industries, Ltd., catalog number: 066-05265)/aluminum. The obtained filtrate was concentrated to obtain an oily substance. The obtained oily substance was purified by silica gel column chromatography. Toluene was used as a developing solvent. The obtained distillate was concentrated to obtain 7.9 g of the target compound as a white solid with a yield of 66%. The following formula (B-5) shows the synthesis scheme of step 5.

<Step 6; Synthesis of di-μ-chloro-tetrakis{2-[1-(2,6-diisobutylphenyl)-1H-naphtho[1,2-d]imidazol-2-yl-κN3]phenyl-κC}diiridium(III) (abbreviated as [Ir(pni-diBup) ₂ Cl] ₂ )> 3.3 g (7.7 mmol) of 1-(2,6-diisobutylphenyl)-2-phenyl-1H-naphtho[1,2-d]imidazole (abbreviated as Hpni-diBup) synthesized in Step 5, 1.6 g (3.7 mmol) of iridium chloride monohydrate, 30 mL of 2-ethoxyethanol, and 10 mL of water were placed in a 100 mL round-bottom flask, and the air in the flask was replaced with hydrogen. The reaction vessel was irradiated with microwaves (2.45 GHz, 100 W) for 2 hours to initiate a reaction. After the reaction, the reaction solution was filtered by suction to obtain 2.8 g of the target compound as a yellow solid with a yield of 69%. The following formula (B-6) shows the synthesis scheme of step 6.

<Step 7; Synthesis of tri{2-[1-(2,6-diisobutylphenyl)-1H-naphtho[1,2-d]imidazol-2-yl-κN3]phenyl-κC}iridium(III) (abbreviated as [Ir(pni-diBup) ₃ ])> 2.0 g (0.92 mmol) of di-μ-chloro-tetrakis{2-[1-(2,6-diisobutylphenyl)-1H-naphtho[1,2-d]imidazol-2-yl-κN3]phenyl-κC}diiridium(III) (abbreviated as [Ir(pni-diBup) ₂ Cl] ₂ ) synthesized by the method of Steps 1 to 6 and 150 mL of dichloromethane were placed in a 500 mL three-necked flask and stirred under a nitrogen flow. To the mixed solution, a mixed solution of 0.72 g (2.8 mmol) of silver trifluoromethanesulfonate and 150 mL of methanol was dropped, and the mixture was stirred in the dark for 3 days. After the reaction was allowed to proceed for a specified time, the reaction mixture was filtered through diatomaceous earth. The filtrate obtained was concentrated to obtain 2.7 g of a yellow solid. The obtained solid 2.7 g, 50 mL of ethanol, and 1.6 g (3.7 mmol) of 1-(2,6-diisobutylphenyl)-2-phenyl-1H-naphtho[1,2-d]imidazole (abbreviated as: Hpni-diBup) synthesized by the method of steps 1 to 5 were placed in a 500 mL eggplant-shaped flask, and heated to reflux for 20 hours under a nitrogen flow. After the reaction was allowed to proceed for a specified time, the reaction mixture was filtered by suction to obtain a solid. The obtained solid was dissolved in dichloromethane and filtered by attraction through diatomaceous earth/neutral silica gel/diatomaceous earth. The obtained filtrate was concentrated to obtain a solid. The obtained solid was purified by silica gel column chromatography. Dichloromethane:hexane=1:3 was used as the developing solvent. The obtained distillate was concentrated to obtain a solid. The obtained solid was recrystallized using ethyl acetate/hexane to obtain 1.1 g of a solid at a yield of 40%. The following formula (B-7) shows the synthesis scheme.

1.1 g of the obtained solid was purified by gradient sublimation. The obtained solid was heated at 340°C for 41 hours under the conditions of a pressure of 2.6 Pa and a hydrogen flow rate of 10.5 mL/min for sublimation purification. After sublimation purification, 0.93 g of a yellow solid was obtained at a recovery rate of 88%.

The yellow solid obtained above was subjected to proton NMR ( ¹ H-NMR) measurement. The obtained values are shown below. In addition, FIG47 shows the ¹ H-NMR spectrum. FIG47 shows that Ir(pni-diBup) ₃ of the organometallic complex of one embodiment of the present invention was obtained.

¹ H-NMR.δ(CD ₂ Cl ₂ ):0.15(d, 9H), 0.39-0.42(m, 18H), 0.59(d, 9H), 1.27-1.35(m, 3H), 1.78-1.86(m, 3H), 1.93-2.02(m, 6H), 2.33(d, 6H), 6.35-6.40(m, 6H), 6.56-6.61(m, 6H), 7.04-7.07(m, 6H), 7.16(t, 3H), 7.25(d, 3H), 7.30(t, 3H), 7.40(d, 3H), 7.48(d, 3H), 7.63(t, 3H), 7.73(d, 3H).

(Reference Example 3) In this reference example, a method for synthesizing Ir(pni-diBup) ₂ (mdppy), which is an example of the phosphorescent material having a five-membered ring used in Example 1, is described.

<Step 1; Synthesis of bis{2-[1-(2,6-diisobutylphenyl)-1H-naphtho[1,2-d]imidazol-2-yl-κN3]phenyl-κC}[2-(4-methyl-5-phenyl-2-pyridyl-κN2)phenyl-κC]iridium(III) (abbreviated as [Ir(pni-diBup) ₂ (mdppy)])> 1.3 g (0.9 mmol) of [Ir(mdppy) ₂ Cl] ₂ and 180 mL of dichloromethane were placed in a 500 mL three-necked flask and stirred under a nitrogen flow. A mixed solution of 0.7 g (2.7 mmol) of silver trifluoromethanesulfonate and 35 mL of methanol was added dropwise to the mixed solution, and the mixture was stirred in a dark place for 18 hours. After the specified time of reaction, the reaction mixture is filtered through diatomaceous earth. The filtrate obtained is concentrated to obtain 1.9 g of a yellow solid. The obtained yellow solid 1.9 g, methanol 30 mL, ethanol 30 mL, Hpni-diBup 1.6 g (3.6 mmol) are placed in a 300 mL eggplant-shaped flask and heated to reflux for 23 hours under a nitrogen flow. After the specified time, the reaction mixture is suction filtered to remove insoluble matter, and then the filtrate is concentrated to obtain a solid. 1-butanol 60 mL is added to the obtained solid, and heated to reflux for 22 hours under a nitrogen flow. After the specified time of reaction, the reaction mixture is suction filtered to obtain a solid. The obtained solid was purified by silica gel column chromatography. A mixed solvent of hexane: dichloromethane = 3:1 was used as the developing solvent. The obtained distillate was concentrated to obtain a solid. The obtained solid was recrystallized using ethyl acetate/hexane to obtain 0.20 g of the target yellow solid at a yield of 9%. The following formula (C-1) shows the synthesis scheme.

0.19 g of the obtained solid was purified by gradient sublimation. The obtained solid was heated at 320°C for 18 hours under the conditions of a pressure of 2.5 Pa and a hydrogen flow rate of 10.3 mL/min for sublimation purification. After sublimation purification, 0.14 g of the target yellow solid was obtained at a recovery rate of 72%.

The yellow solid obtained above was subjected to ¹ H-NMR measurement. The obtained values are shown below. In addition, FIG48 shows the ¹ H-NMR spectrum. As can be seen from FIG48, [Ir(pni-diBup) ₂ (mdppy)] of the organometallic complex of one embodiment of the present invention was obtained.

¹ H-NMR.δ(CD ₂ Cl ₂ ):0.09-0.15(m, 9H), 0.29-0.34(m, 9H), 0.40(t, 1H), 0.45(d, 3H), 0.51(d, 3H), 1.18-1.24(m, 1H), 1.34-1.49(m, 1H), 1.70-1.78(m, 1H), 1.88-2.09(m, 6H), 2.17-2.25(m, 2H), 2.51(s, 3H), 6.30-6.40(m, 3H), 6.48(t, 1H), 6.61-6.52(m, 3H), 6.64-6.69(m, 2H), 6.74-6.79(m, 2H), 6.83(t, 1H), 6.93-7.01(m, 3H), 7.08(t, 1H), 7.13-7.25(m, 8H), 7.34-7.51(m, 6H), 7.57-7.73(m, 4H), 7.87(d, 1H), 7.94(s, 1H), 8.31(s, 1H).

(Reference Example 4) This reference example describes the synthesis method of the fluorescent material with a protective group used in Example 2, namely 2,6tBu-mmtBuDPhA2Anth.

1.1 g (2.5 mmol) of 2,6-di-tert-butylanthracene, 2.3 g (5.8 mmol) of bis(3,5-tert-butylphenyl)amine, 1.1 g (11 mmol) of sodium tert-butoxide, and 60 mg (0.15 mmol) of SPhos were placed in a 200 mL three-necked flask, and the air in the flask was replaced with nitrogen. 25 mL of xylene was added to the mixture, and the mixture was degassed under reduced pressure. 40 mg (70 μmol) of bis(dibenzylideneacetone)palladium(0) was added to the mixture, and then the mixture was stirred at 150° C. for 6 hours under a nitrogen flow.

After stirring, 400 mL of toluene was added to the obtained mixture, and then the mixture was suction filtered through magnesium silicate, diatomaceous earth, or alum to obtain a filtrate. The obtained filtrate was concentrated to obtain a brown solid.

The solid was purified by silica gel column chromatography (developing solvent: hexane: toluene = 9:1) to obtain the target yellow solid. The yellow solid was recombined with hexane and methanol to obtain 0.45 g of the target yellow solid with a yield of 17%. The following (D-1) shows the synthesis scheme of step 1.

0.45 g of the obtained yellow solid was purified by gradient sublimation. The yellow solid was heated at 275°C for 15 hours under a pressure of 5.0 Pa for sublimation purification. After sublimation purification, 0.37 g of the target yellow solid was obtained at a recovery rate of 82%.

Note that the measurement results of the yellow solid obtained in the above step 1 using ¹ H-NMR are shown below. In addition, FIG. 56A, FIG. 56B and FIG. 57 show ¹ H-NMR spectra. FIG. 56B is an enlarged view of the range of 6.5 ppm to 9.0 ppm of FIG. 56A. In addition, FIG. 57 is an enlarged view of the range of 0.5 ppm to 2.0 ppm of FIG. 56A. From this result, it can be seen that 2,6tBu-mmtBuDPhA2Anth was obtained.

¹ H-NMR (CDCl ₃ , 300MHz): σ=8.11(d, J=9.3Hz, 2H), 7.92(d, J=1.5Hz, 1H), 7.34(dd, J=9.3Hz, 2.0Hz, 2H), 6.96-6.95(m, 8H), 6.91-6.90(m, 4H), 1.13-1.12(m, 90H).

100:EL layer 101:electrode 102:electrode 106:luminescent unit 108:luminescent unit 111:hole injection layer 112:hole transport layer 113:electron transport layer 114:electron injection layer 115:charge generation layer 116:hole injection layer 117:hole transport layer 118:electron transport layer 119:electron injection layer 120:luminescent layer 130:luminescent layer 131:compound 132 : Compound 133: Compound 134: Compound 135: Compound 150: Light-emitting element 170: Light-emitting layer 250: Light-emitting element 301: Guest material 302: Guest material 310: Light-emitting body 320: Protective base 330: Host material 601: Source side drive circuit 602: Pixel part 603: Gate side drive circuit 604: Sealing substrate 605: Sealing agent 607: Space 6 08: Wiring 610: Substrate 611: Switching TFT 612: Current Control TFT 613: Electrode 614: Insulator 616: EL layer 617: Electrode 618: Light-emitting element 623: n-channel TFT 624: p-channel TFT 900: Portable information terminal 901: Casing 902: Casing 903: Display unit 905: Hinge unit 910: Portable information terminal 911: External Case 912: Display 913: Operation button 914: External connection port 915: Speaker 916: Microphone 917: Camera 920: Camera 921: Case 922: Display 923: Operation button 924: Shutter button 926: Lens 1001: Substrate 1002: Base insulation film 1003: Gate insulation film 1006: Gate electrode 1007: Gate electrode 1008: Gate Electrode 1020: Interlayer insulating film 1021: Interlayer insulating film 1022: Electrode 1024B: Electrode 1024G: Electrode 1024R: Electrode 1024W: Electrode 1025B: Lower electrode 1025G: Lower electrode 1025R: Lower electrode 1025W: Lower electrode 1026: Partition wall 1028: EL layer 1029: Electrode 1031: Sealing substrate 1032: Sealing Agent 1033: Base material 1034B: Color layer 1034G: Color layer 1034R: Color layer 1036: Protective layer 1037: Interlayer insulation film 1040: Pixel part 1041: Drive circuit part 1042: Edge part 1044R: Red pixel 1044G: Green pixel 1044B: Blue pixel 1044W: White pixel 2100: Robot 2101: Illuminance sensor 2102 : Microphone 2103: Upper camera 2104: Speaker 2105: Display 2106: Lower camera 2107: Obstacle sensor 2108: Moving mechanism 2110: Computing device 5000: Housing 5001: Display 5002: Display 5003: Speaker 5004: LED light 5006: Connector 5007: Sensor 5008: Microphone 5012: Support 5013: Headphones 5100: Sweeping robot 5101: Display 5102: Camera 5103: Brush 5104: Operation button 5120: Trash 5140: Portable electronic device 5150: Portable information terminal 5151: Housing 5152: Display area 5153: Bending part 8501: Lighting device 8502: Lighting device 8503: Lighting device 8504: Lighting device

In the drawings: [FIG. 1A] and [FIG. 1B] are schematic cross-sectional views of a light-emitting layer of a light-emitting element of an embodiment of the present invention. [FIG. 1C] is a diagram illustrating the energy level correlation of a light-emitting element of an embodiment of the present invention. [FIG. 2A] is a schematic view of a known guest material. [FIG. 2B] is a schematic view of a guest material used in a light-emitting element of an embodiment of the present invention. [FIG. 3A] is a structural formula of a guest material used in a light-emitting element of an embodiment of the present invention. [FIG. 3B] is a ball-and-stick diagram of a guest material used in a light-emitting element of an embodiment of the present invention. [FIG. 4A] is a schematic cross-sectional view of a light-emitting layer of a light-emitting element of an embodiment of the present invention. [FIG. 4B] and [FIG. 4C] are diagrams illustrating the energy level correlation of a light-emitting element of an embodiment of the present invention. [FIG. 5A] is a schematic cross-sectional view of a light-emitting layer of a light-emitting element of an embodiment of the present invention. [FIG. 5B] and [FIG. 5C] are diagrams illustrating the energy level correlation of the light-emitting layer of a light-emitting element of an embodiment of the present invention. [FIG. 6] is a schematic cross-sectional view of a light-emitting element of an embodiment of the present invention. [FIG. 7A] is a top view of a display device of an embodiment of the present invention. [FIG. 7B] is a schematic cross-sectional view of a display device of an embodiment of the present invention. [FIG. 8A] and [FIG. 8B] are schematic cross-sectional views of a display device of an embodiment of the present invention. [FIG. 9A] and [FIG. 9B] are schematic cross-sectional views of a display device of an embodiment of the present invention. [FIG. 10A] to [FIG. 10D] are three-dimensional diagrams of a display module according to an embodiment of the present invention. [FIG. 11A] to [FIG. 11C] are diagrams of an electronic device according to an embodiment of the present invention. [FIG. 12A] and [FIG. 12B] are three-dimensional diagrams of a display device according to an embodiment of the present invention. [FIG. 13] is a diagram of an illumination device according to an embodiment of the present invention. [FIG. 14] is a diagram illustrating the external quantum efficiency-brightness characteristics of a light-emitting element according to an embodiment. [FIG. 15] is a diagram illustrating the electroluminescence spectrum of a light-emitting element according to an embodiment. [FIG. 16] is a diagram illustrating the external quantum efficiency-brightness characteristics of a light-emitting element according to an embodiment. [FIG. 17] is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to the embodiment. [FIG. 18] is a diagram illustrating the external quantum efficiency-brightness characteristics of the light-emitting element according to the embodiment. [FIG. 19] is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to the embodiment. [FIG. 20] is a diagram illustrating the external quantum efficiency-brightness characteristics of the light-emitting element according to the embodiment. [FIG. 21] is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to the embodiment. [FIG. 22] is a diagram illustrating the external quantum efficiency-brightness characteristics of the light-emitting element according to the embodiment. [FIG. 23] is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to the embodiment. [FIG. 24] is a diagram illustrating the external quantum efficiency-brightness characteristics of the light-emitting element according to the embodiment. [FIG. 25] is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to the embodiment. [FIG. 26] is a diagram illustrating the external quantum efficiency-brightness characteristics of the light-emitting element according to the embodiment. [FIG. 27] is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to the embodiment. [FIG. 28] is a diagram illustrating the external quantum efficiency-brightness characteristics of the comparative light-emitting element according to the embodiment. [FIG. 29] is a diagram illustrating the electroluminescence spectrum of the comparative light-emitting element according to the embodiment. [FIG. 30] is a diagram illustrating the relationship between the emission spectrum and the absorption spectrum according to the embodiment. [FIG. 31] is a diagram illustrating the relationship between the emission spectrum and the absorption spectrum according to the embodiment. [Figure 32] is a diagram illustrating the relationship between the emission spectrum and the absorption spectrum according to the embodiment. [Figure 33] is a diagram illustrating the relationship between the emission spectrum and the absorption spectrum according to the embodiment. [Figure 34] is a diagram illustrating the relationship between the emission spectrum and the absorption spectrum according to the embodiment. [Figure 35] is a diagram illustrating the relationship between the emission spectrum and the absorption spectrum according to the embodiment. [Figure 36] is a diagram illustrating the relationship between the emission spectrum and the absorption spectrum according to the embodiment. [Figure 37] is a diagram illustrating the relationship between the external quantum efficiency and the guest material concentration according to the embodiment. [Figure 38] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 39] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 40] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 41] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 42] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 43] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 44] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 45A] and [Figure 45B] are diagrams illustrating the NMR spectrum of the compound according to the reference example. [Figure 46] is a diagram illustrating the NMR spectrum of the compound according to the reference example. [Figure 47] is a diagram illustrating the NMR spectrum of the compound according to the reference example. [Figure 48] is a diagram illustrating the NMR spectrum of the compound according to the reference example. [Figure 49] is a diagram illustrating the measurement results of the luminescence life of the light-emitting element according to the embodiment. [Figure 50] is a diagram illustrating the measurement results of the luminescence life of the light-emitting element according to the embodiment. [Figure 51] is a diagram illustrating the measurement results of the luminescence life of the light-emitting element according to the embodiment. [Figure 52] is a diagram illustrating the external quantum efficiency-brightness characteristics of the light-emitting element according to the embodiment. [Figure 53] is a diagram illustrating the electroluminescence spectrum of the light-emitting element according to the embodiment. [Figure 54] is a diagram illustrating the results of the reliability test according to the embodiment. [Figure 55] is a diagram illustrating the measurement results of the luminescence life of the light-emitting element according to the embodiment. [Figure 56A] and [Figure 56B] are diagrams showing the NMR spectra of the compounds according to the reference examples. [Figure 57] is a diagram showing the NMR spectra of the compounds according to the reference examples.

Claims (18)

A light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer includes a first material, a second material, and a third material, wherein the first material is a metal complex capable of converting triplet excitation energy into light emission and having a five-membered ring skeleton, the second material is capable of converting singlet excitation energy into light emission and having a light-emitting body and five or more protective groups, the light-emitting body is a fused aromatic ring or a fused heteroaromatic ring, the five or more protective groups independently have any one of an alkyl group having 3 or more and 10 or less carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more and 10 or less carbon atoms, and a trialkylsilyl group having 3 or more and 12 or less carbon atoms, the third material has a diazine skeleton or a triazine skeleton, and the T1 energy level of the first material is higher than the S1 energy level of the second material. According to claim 1, at least four of the five or more protecting groups are independently any one of an alkyl group having 3 or more and 10 or less carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more and 10 or less carbon atoms, and a trialkylsilyl group having 3 or more and 12 or less carbon atoms. A light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer comprises a first material, a second material and a third material, wherein the first material is a metal complex capable of converting triplet excitation energy into light emission and having a five-membered ring skeleton, wherein the second material is capable of converting singlet excitation energy into light emission and having a light emitter and at least four protecting groups, wherein the light emitter is a fused aromatic ring or a fused heteroaromatic ring, wherein the four protecting groups are not directly bonded to the third material. In the fused aromatic ring or the fused heteroaromatic ring, the four protecting groups independently have any one of an alkyl group having 3 or more and 10 or less carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more and 10 or less carbon atoms, and a trialkylsilyl group having 3 or more and 12 or less carbon atoms, the third material has a diazine skeleton or a triazine skeleton, and the T1 energy level of the first material is higher than the S1 energy level of the second material. A light-emitting element including a light-emitting layer between a pair of electrodes, wherein the light-emitting layer comprises a first material and a second material, the first material is a metal complex having a five-membered ring skeleton and capable of converting triplet excitation energy into light-emitting, the second material is capable of converting singlet excitation energy into light-emitting, the second material has a light-emitting body and two or more diarylamine groups, the light-emitting body is a fused aromatic ring or a fused heteroaromatic ring, the fused aromatic ring or the fused heteroaromatic ring Bonded to the two or more diarylamine groups, the aryl groups in the two or more diarylamine groups each independently have at least one protecting group, the protecting group having any one of an alkyl group having 3 or more and 10 or less carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 or more and 10 or less carbon atoms, and a trialkylsilyl group having 3 or more and 12 or less carbon atoms, and the T1 energy level of the first material is higher than the S1 energy level of the second material. According to the light-emitting element of claim 4, the aryl groups in the two or more diarylamine groups each independently have at least two protecting groups. According to the light-emitting element of claim 4, the diarylamine group is a diphenylamine group. According to the light-emitting element of claim 4, the light-emitting layer further comprises a third material, and the third material has a diazine skeleton or a triazine skeleton. According to claim 1, at least one of the atoms constituting the five or more protecting groups is located directly on the surface of one of the fused aromatic ring and the fused heteroaromatic ring, and at least one of the atoms constituting the five or more protecting groups is located directly on the surface of the other of the fused aromatic ring and the fused heteroaromatic ring. According to the light-emitting element of claim 6, the phenyl groups in the two or more diphenylamine groups have protective groups at the 3-position and the 5-position, respectively and independently. A light-emitting element according to any one of claims 1, 3 and 4, wherein the five-membered ring skeleton has any one of a pyrazole skeleton, an imidazole skeleton and a triazole skeleton. According to the light-emitting element of claim 10, the nitrogen atoms unrelated to the double bond of the imidazole skeleton and the triazole skeleton are bonded to a substituted or unsubstituted aromatic group having 6 to 13 carbon atoms. A light-emitting element according to any one of claims 1, 3 and 4, wherein the alkyl group is a branched alkyl group. The light-emitting element according to any one of claims 1, 3 and 4, wherein the fused aromatic ring or the fused heteroaromatic ring comprises naphthalene, anthracene, fluorene,

, triphenylmethane, tetraphenylmethane, pyrene, perylene, coumarin, quinacridone and naphthodibenzofuran. A light-emitting element according to claim 1 or 3, wherein the first material and the third material form an excited state complex. According to the light-emitting element of claim 4, the light-emitting layer also has a third material, and the first material and the third material form an excited state complex. A light-emitting element according to any one of claims 1, 3 and 4, wherein the emission spectrum of the first material overlaps with the absorption band on the longest wavelength side of the second material. An electronic device comprising: a light-emitting element according to any one of claims 1, 3 and 4; and at least one of a housing and a touch sensor. A lighting device comprises: a light-emitting element according to any one of claims 1, 3 and 4; and at least one of a housing and a touch sensor.

Images